help with subsonic 308 rounds
- Thread starter Rschmidy
- Start date
Trail Boss is a good choice thanks to its volume. The faster your barrel twist the better. I'd say at least a 1:10 to stabilize your 185s. Faster if you go heavier. I've had decent luck with Trail Boss, 170 and 200 grain bullets in my 1:10 308. I'm not opening up the flash holes or using magnum primers. I do put a light crimp on them though. Accuracy seems to be around 1.5-2.5 MOA, but I do see flyers and some vertical stringing usually on the first couple of cold bore shots that opens up the group averages past the 1.5-2.5 range. After that it tends to settle in. My 300 Blackout 1:7 is more consistent. I'm interested in hearing others experiences as well.
**Test all your loads without your can first!!! Make sure you're getting nice round holes in the target (no key holes).
**Test all your loads without your can first!!! Make sure you're getting nice round holes in the target (no key holes).
i've read in the other subsonic threads that folks are also using tightgroup, h110, and red or green dot too. i haven't tinkered yet, but did pick up some trailboss last week for spring / summer tinkering (if spring ever does come here in the NE).
i copied and pasted some of the loads and tips extracted in other threads for myself on the side, below is what i got, maybe it'll help you out too:
Powders suitable for subsonic loads include: N310, N312, Bullseye, Clays, Titewad, HP38 and Red Dot. There are other suitable powders available but these are the best to start out with. Red Dot is probably the best powder to work with because it gives the highest load densities. The Vihtavuori powders (N310 and N312) are particularly interesting because they burn very quickly and cleanly and they exhibit exceptionally stable performance over an extremely wide range of environmental temperatures.
1. Get a chronograph, it is useless to develop a load without one.I can't stress this enough, if you are loading subsonic ammo without one then you wasting your time and money, period. You need to be between 1000 and 1100 feet per second. Too slow and you run the risk of inadequate stability and excessive arc on the trajectory; too fast and you go supersonic with the associated additional noise. The speed of sound varies with temperature. Speed of sound temperature air formula without no barometric pressure calculator table air density of air calculation mach 1 acoustic impedance propagation air density sea level velocity ideal gas 20 degrees or 21 degrees Celsius C cold warm - sengpi At 32F it is about 1087 fps, at 90F it is about 1149 fps at -40F it is only 1004 fps. Quiet loads made for southern Texas summers are going to be loud in an Alaskan winter.
2. Use magnum primers, the extra heat makes the powder burn more consistently.
3. Just about any magnum pistol powder will work well. I use WC820 (like H110). It burns well even when the case is less than half full and I have never had any detonation issues. I think detonation is a myth and is actually caused by double loads or firing the next round with a squib stuck in the barrel.
4. There is very little to gain with using expensive heavy match grade bullets compared to round nose bullets. At subsonic speeds the higher BC of the pointed bullets are only a tiny bit more streamlined than the round nose bullets. The slow speed still requires that the shooter knows the range to the target precisely no matter what rifle bullet is used.
For example, a 180 grain 30 caliber match bullet has a BC of about .5, a 220 RN .4, a 45 caliber 230 grain .2. Given a zero of 200 yards the match bullet will be 16.5" high at 100 yards, the 220 RN 16.8" high and the 45 cal bullet will be only 18.5" high. The round nose bullets work well.
I have found that using a 147-168 grain FMJ boat tail bullet in a subsonic 308 or 300 blackout/whisper results in poor accuracy. The longer 220 and 240 grain match bullets work very well with a 1-8 twist probably due to the longer bearing surface. Military ball bullets especially suck.
5. Using a cartridge like the 223 or 308 that is designed for a high speed light weight bullet will ensure that a subsonic bullet will never match the accuracy of the standard load. If you want a subsonic 30 caliber that is accurate, use the 300 blackout, if you want versatility, then use the 308.
6. Ballistic calculations that tell you if a bullet will be stable for a certain velocity and twist are only worth the paper they are printed on. The only thing that counts is the size of the group and the shape of the hole they make in a target at least 100 yards away.
I have found that 180 grain RN bullets work well with a 1-12 twist and a 1-10 twist will work up to 220 RN. A 1-8 twist will work on anything up to 240 grain hpbt. If accuracy sucks with your load, then it is probably yawing and you shouldn't use it with a silencer.
1. As Ranb suggests " The only thing that counts is the size of the group and the shape of the hole they make in a target at least 100 yards away" but with one additional caveat when the subject at hand is hunting. There has to be some reasonable amount of residual force left in the round at impact. That said, the best solution allows for the use of the heavier (heaviest) roundnose bullets at ranges that are, in my opinion, within 125 yards. Chrony is a must, especially with any position sensitive powder. I went the .308 subsonic, .260 subsonic and 6.8 subsonic route.
Also, for your review and consideration:
Safely Develop and Load Subsonic Ammunition "The loading of subsonic ammunition should not be undertaken lightly. Done incorrectly or by the incautious or inexperienced, it presents a significant risk of grievous bodily harm to the shooter."
The goal is to explain techniques used to safely develop and load subsonic ammunition without risking life and limb. The ultimate danger in subsonic loading is a phenomenon known as Secondary Explosive Effect (SEE). SEE can destroy the strongest rifle action and it can happen on the first shot or the tenth. In fact it is more likely to happen after the bore is dirty from the first few shots. SEE is the result of slow or incomplete ignition of small amounts of smokeless powder. The powder smolders and releases explosive gases which, when finally ignited, detonate in a high order explosion. The warning sign for imminent SEE is a hangfire or delayed ignition.There are a number of techniques that can be used to prevent or delay the onset of SEE. These involve specially prepared cases as well as bullets, in addition to selecting a suitable powder and primer. Lets begin with the easy stuff. All reduced velocity loads should start with a magnum primer. The hotter and longer duration flame ensures the small powder charge lying in the bottom of a large rifle case is properly ignited. Testing revealed that accuracy is increased 8% with magnum primers. Reloading manuals contain minimum powder charges for a reason. Going much below the minimum load with a slow burning rifle powder can trigger SEE. Subsonic loads use fast burning pistol powders, the faster the better. This ensures the powder is easy to ignite and will be totally consumed before the bullet leaves the muzzle. Not only is this safer but it is quieter as well. Quieter is always good when operating in the subsonic realm. A secondary consideration when choosing a powder is its bulk density. That is the amount of volume a given weight of powder will occupy in the case. Bulk densities are typically measured in grains per cubic inch; with the lower number meaning the powder is more voluminous. Fluffy (low bulk density) powders like Red Dot take up much more room in the case. Load density is safety in a subsonic load. It is suggested that loads never go below 30 percent load density (powder occupies 30 percent of the case volume) unless you want to dance with the devil and the deep blue SEE.
Load density can be measured by dropping a length of wood dowel into the loaded case. Mark the dowel where it meets the case mouth. Then pull the dowel out and compare it against the case. Keep notes on load densities for every powder and case combination so that safe loads can be identified at a glance before they are loaded. Don't go below 30% load density!
Powders suitable for subsonic loads include: N310, N312, Bullseye, Clays, Titewad, HP38 and Red Dot. There are other suitable powders available but these are the best to start out with. Red Dot is probably the best powder to work with because it gives the highest load densities. The Vihtavuori powders (N310 and N312) are particularly interesting because they burn very quickly and cleanly and they exhibit exceptionally stable performance over an extremely wide range of environmental temperatures.
Powder burn rates are important because the low pressures generated by subsonic loads are typically not sufficient to properly seal the case in the chamber. Faster powders create better sealing and less sooty blow-by on the outside of the case. Once the powder choice has been made, the next step is to select and prepare the bullets. Bullet choice for subsonic shooting is much more critical than for conventional ammunition. Low velocity greatly reduces the projectile's rotational rate (RPM) and thus stability. Fast twist barrels are essential to successful subsonic loads. In .30 calibre this means a 1:10 twist or faster. A 1:10 twist will stabilize a 220 grain round-nose bullet at 950 fps. Computer programs that calculate projectile stability are available free on the Internet. These calculators usually quote a Stability Factor (SF) of 1.3 for full stabilization in a conventional load. It has been found through testing that a SF in the range of 2.0 to 2.2 or greater is needed for a bullet to fully stabilize at subsonic velocity. This depends on how well the bullet is balanced with its center of mass. Lapua makes a special subsonic 200 grain .30 caliber bullet that is stable with a SF of only 1.36.
To prevent bullets sticking in a dirty bore, all conventional jacketed bullets used for subsonic loads must be lubricated. There are two primary methods of achieving proper lubrication. The traditional method is to dip the bullets in melted, refined animal fats (lard). The fat hardens as it cools, leaving a thin, slick surface on the bullet. The downside is this method is messy and slow. The modern method is to simply use moly coated bullets. Moly is easy to get and can be applied to bullets by the hundreds in only a few hours. Moly coated bullets are also available direct from the factory. Moly coated bullets were used exclusively in testing for this article and the author has never had a coated bullet stick. The same cannot be said for uncoated bullets. As a side note, cast lead bullets are inherently lubricated and do not need to be coated. One final note on bullets for subsonic loads. Never crimp and don't seat bullets into the lands. Bullets should be seated with lots of jump for safe operation. The most radical modification required for safe subsonic ammunition comes in the case preparation. To take advantage of the magnum primer, the flash-hole should be drilled out to 9/64 inch (3.5mm) for a large-rifle primer. The enlarged flash hole allows as much of the primer flash as possible to reach the powder. This is especially important in full sized rifle cases. It also helps to prevent primer setback due to the low operating pressure of these rounds. DO NOT use subsonic modified cases for full power ammunition! Now that all the components are gathered and properly prepared, we are ready to begin to develop ammunition. Unfortunately this is where things get difficult. There is almost no published subsonic load data anywhere. It is almost unheard of in any load manuals and it is fairly scarce on the Internet. A starting or reference point is needed to work from to avoid operating blind in the dark, which is not a good place to be when dealing with potentially explosive components. CE Harris developed a fairly well known reduced power load known as "The Load." Information on "The Load" can be found fairly easily in an Internet search. To throw the reader a bone, here are the basics. "The Load" can be used in any full sized rifle case without any modifications to the components. It consists of 13 grains of Red Dot (greater than 50 percent load density in .30-06 case) driving a lightweight bullet (125 grain in a .30 caliber) at medium velocity (approximately 1,600 fps). The smart and experienced reloader should be able to extrapolate a safe starting load for heavy bullets from The Load. Keep in mind it is better to start a bit fast and work the velocities down slowly remembering NEVER to go below the 30 percent load density rule (It really should be a Law!)When using a medium to small sized case, it is possible to compare internal volumes with other cases to find suitable starting data. For example the author discovered the .44 Magnum case (with a bullet seated) has almost the same internal volume as the 7.62x39mm case. All sorts of .44 Magnum load data exists for 180 to 220 grain bullets from which safe starting subsonic loads can be extrapolated. Once the first test loads are assembled, it is time to head to the range and see how they work. A chronograph is essential to developing safe subsonic loads. Don't even try it if you don't have access to one. The target velocity to work towards should be 50-100 fps less than the speed of sound or about 950 fps. This puts velocity below the transonic range where the supersonic crack begins to be generated. The sonic crack is not generated at exactly the speed of sound. The sound increases in volume across the transonic range starting about 92-93 percent of the speed of sound based upon research by Al Paulson. Also keep in mind that a sound suppressor (silencer) may create about 30 fps of freebore boost, which in turn argues for lowering projectile velocity an additional 30-50 fps. At about 50 fps above the speed of sound the sonic crack reaches maximum volume. During the initial testing period, it is important to start with a clean and lightly lubed bore to ensure bullets slip down the barrel easily. The bore should be lubed after every 2 or 3 shots to keep it clean and slippery. Velocities will vary somewhat due to the oil in the bore but at this point safety is more important than consistency. Make sure the bullet leaves the bore after every shot. Most of the time it is possible to hear the slow moving bullet hit the target but if need be physically check the bore. A stuck bullet will ruin your barrel and the day. The first range session should be all about finding a safe load that meets the 950 fps requirement. It is certainly possible to go much slower than this but the danger of triggering SEE does not warrant the slight reduction in muzzle signature.
Subsonics are very sensitive to barrel condition and fouling. Velocities can vary considerably depending on how clean the barrel is. Temperature can also have a great effect on subsonic muzzle velocity. Once a safe load or two in the desired velocity range has been found, a second range session can be used to test the effects of reducing the bore lubing frequency as well as the consistency and trajectory of the load. Subsonic loads require the shooter pay attention at all times. A stuck bullet is always possible, with predictable results. Always remember a hangfire or delayed ignition signals impending SEE. To easily distinguish modified cases (and subsonic ammunition) from conventional rounds, use a blue indelible felt marker to color either the case extractor groove or the case head. The blue case head (right) is more traditional and is still used by Lapua for their subsonic ammunition. The author prefers the blue extractor groove (below, right) because it is easier to see when handling ammunition and doesn't rub off as easily. Once you become comfortable loading and shooting subsonic ammunition you will find that they are a lot of fun to shoot. There is hardly any recoil and muzzle signature is reduced to a slight pop. Shooting without hearing protection is comfortable and it is even possible to hear the bullet hit the target with a loud "Thwack!"
Rules for the safe operation of subsonic loads:
1. Drill Flashole to 3.5mm (9/64") to allow all the primer flash to enter the case and ignite the powder completely.
2. Use Magnum Primers for maximum primer flash and better powder ignition.
3. Lube all bullets. Moly is good, animal fat is better.
4. Lubricate the bore regularily while shooting.
5. Never crimp bullets into cases. Never seat bullets "into the lands."
6. Try not to use powder charges of less than 40% load density.
7. If load density is less than 40%, use tamping or fillers to keep the powder at the bottom of the case.
8. Make sure the bullet exits the bore after each shot.
9. Use only the fastest burning pistol powders - N310, N312, Bullseye, Clays, Titewad, HP38, Red Dot.
10. Any sort of slow ignition or hangfire is a warning of iminent Secondary Explosive Effect (SEE).
Always mark subsonic cases so that they are NEVER USED FOR SUPERSONIC PRESSURES.
16" Krieger 1/10
220 Hornady RNSP
10.7 gr of Trail boss
1040 fps
mag primers, win cases
3/4-1" groups at 100
not temp sensitive or powder position sensitive
slightly louder than loads with Green dot or other pistol powders, but more reliable.
200 gr Lapua Subsonic, 8.2 gr Red Dot, WLRM, 2.20" O2H
950 fps @ 90F
200 gr Lapua Subsonic, 10.0 gr Trail Boss, WLRM, 2.20" O2H
967 fps @ 70F
Come-ups
100 yds, 4.2 mil
200 yds, 9.2 mil
280 yds, 14.2 mil
Remington M700, 16" 1/10", War Tech Tensioned Barrel System w/ST Black Star 8" installed, H&S 5R stock and bottom metal, Leupold MK4 1-piece base, Leupold MK4 1" Medium alloy rings, Bushnell 3200 10x40:
Case: Federal Gold Medal
Primer: CCI 200 Large Rifle
Powder: IMR Trail Boss
Bullet: Sierra 170gr (30-30) bullet .308 dia. #2010
Starting Load: 9.0gr (980 fps average)
Work Up: loaded to 9.8 (1017 fps average)
Accuracy Load: so far most producing Sub-MOA
Basic Dope:
0'd @ 50yd
75 - 2.25MOA
100 - 4.5MOA
125 - 7.0MOA
150 - 9.5MOA
Note: this is a fun target load that is less expensive and @ 200yds has been a killer on 8oz. water bottles. this is also a load that has been proven lethal to 102yds for the average Whitetail or rather large gray squirells that are considered armed and dangerous! Will update with more results with better weather conditions which will permit Chrony and groups, stay tuned.
1/10 twist, 18" Krieger
220 Hornady RNSP
Win Mag Primers
2.8"
10.5 Greendot
1 ragged hole at 100m
2" grp at 200m
Same as above w/10gr Trail boss
1" at 100
3.5" at 200
30 CAL Twist rate:
1/12: 180 grain and below for the SMK types designes (AMAXs, FMJ, anything with a pointed tip and boattail) 190's with a RN design
1/10: 200 and below for pointed designs, 220 for RN designs
1/8: 240 and below for pointed design, I don't know of a 30 cal round nose design greater than 220.
Using a 223 subsonic is no different that a .22 subsonic, just more expensive. Bullet weights are similar and the velocities are the same. Besides, to get sub 223 loads you have to do a lot of researching for the right load and spend an awfull lot of time prepping the rounds. For .22, just stop by walmart...
If you want to go after 223 subs, I used greendot with about 8 grains. That was back in 2000, now I'd try trailboss, SR 4759, or RE7.
For powder in a 308:
Pistol powders are more quiet (2-4dB which is barely audible to the ear). However, they have several drawbacks:
1. Extremely small case capacity which leads to significant velocity spreads due to position sensitivity. For example, above, I'm quoted with a load for greendot. While the accuracy was excellent, I had to make sure I did tilted the barrel up and tapped the rifle to seat the powder against the primer for every shot to get those groups.
2. They are very temp sensitive
3. A doubled charge (or even one that's just a few grains over) will quickly create a pressure spike and can lead to the case failing
For the bulkier powders (TB, 4759, RE7, Accurate 2250 ro somehting like that.. not sure but it's labeled as a bulky powder for low power loads) , just add a little water to the can to surpass the suppression level of the pistol powders. Click...wait...wait...wait...thump is what you get.
Trail Boss isn't the universal holy grail for subsonic rilfe loads but it's a great place to start. For 308s with barrels over 16", start around 10 grains. I haven't found enough evidence that there is a temp sensitivity, but there certainly isn't a case position sentisitivity. With the heavier 220-240 gr bullets, I've had a hard time getting them to 1050 with TB in my pistol. Consequently, I played around and found IMR SR 4759 and have been very happy with it from 5-65 deg.
Others are playing with H110 and CLAYS, but the same problems arise as with the pistol powders.
For primers, I always use mag primers, but they might not be necessary with Trail Boss or other bulky powders. I am convinced that they are the safest decision when using pistol or shotgun powders due to the small case capacity
Savage 10fp .308 1-10 twist factory 24" barrel
170 grain harnady fp
Federal brass full lenth sized
Winchester lr mag primers
9.5 grains of red dot
It's done a half inch so far at 100
308 Win. 26" bbl 1/11 twist, GAP Palma chamber.
Hornady 180 RN
Lapua brass
CCI BR2
10.2gr. Trailboss
2.650" COAL
1030fps @ 80*F
Hornady 180 RN
Lapua brass
CCI BR2
8.0gr. Titegroup
2.650" COAL
1040fps @ 80*F
i copied and pasted some of the loads and tips extracted in other threads for myself on the side, below is what i got, maybe it'll help you out too:
Powders suitable for subsonic loads include: N310, N312, Bullseye, Clays, Titewad, HP38 and Red Dot. There are other suitable powders available but these are the best to start out with. Red Dot is probably the best powder to work with because it gives the highest load densities. The Vihtavuori powders (N310 and N312) are particularly interesting because they burn very quickly and cleanly and they exhibit exceptionally stable performance over an extremely wide range of environmental temperatures.
1. Get a chronograph, it is useless to develop a load without one.I can't stress this enough, if you are loading subsonic ammo without one then you wasting your time and money, period. You need to be between 1000 and 1100 feet per second. Too slow and you run the risk of inadequate stability and excessive arc on the trajectory; too fast and you go supersonic with the associated additional noise. The speed of sound varies with temperature. Speed of sound temperature air formula without no barometric pressure calculator table air density of air calculation mach 1 acoustic impedance propagation air density sea level velocity ideal gas 20 degrees or 21 degrees Celsius C cold warm - sengpi At 32F it is about 1087 fps, at 90F it is about 1149 fps at -40F it is only 1004 fps. Quiet loads made for southern Texas summers are going to be loud in an Alaskan winter.
2. Use magnum primers, the extra heat makes the powder burn more consistently.
3. Just about any magnum pistol powder will work well. I use WC820 (like H110). It burns well even when the case is less than half full and I have never had any detonation issues. I think detonation is a myth and is actually caused by double loads or firing the next round with a squib stuck in the barrel.
4. There is very little to gain with using expensive heavy match grade bullets compared to round nose bullets. At subsonic speeds the higher BC of the pointed bullets are only a tiny bit more streamlined than the round nose bullets. The slow speed still requires that the shooter knows the range to the target precisely no matter what rifle bullet is used.
For example, a 180 grain 30 caliber match bullet has a BC of about .5, a 220 RN .4, a 45 caliber 230 grain .2. Given a zero of 200 yards the match bullet will be 16.5" high at 100 yards, the 220 RN 16.8" high and the 45 cal bullet will be only 18.5" high. The round nose bullets work well.
I have found that using a 147-168 grain FMJ boat tail bullet in a subsonic 308 or 300 blackout/whisper results in poor accuracy. The longer 220 and 240 grain match bullets work very well with a 1-8 twist probably due to the longer bearing surface. Military ball bullets especially suck.
5. Using a cartridge like the 223 or 308 that is designed for a high speed light weight bullet will ensure that a subsonic bullet will never match the accuracy of the standard load. If you want a subsonic 30 caliber that is accurate, use the 300 blackout, if you want versatility, then use the 308.
6. Ballistic calculations that tell you if a bullet will be stable for a certain velocity and twist are only worth the paper they are printed on. The only thing that counts is the size of the group and the shape of the hole they make in a target at least 100 yards away.
I have found that 180 grain RN bullets work well with a 1-12 twist and a 1-10 twist will work up to 220 RN. A 1-8 twist will work on anything up to 240 grain hpbt. If accuracy sucks with your load, then it is probably yawing and you shouldn't use it with a silencer.
1. As Ranb suggests " The only thing that counts is the size of the group and the shape of the hole they make in a target at least 100 yards away" but with one additional caveat when the subject at hand is hunting. There has to be some reasonable amount of residual force left in the round at impact. That said, the best solution allows for the use of the heavier (heaviest) roundnose bullets at ranges that are, in my opinion, within 125 yards. Chrony is a must, especially with any position sensitive powder. I went the .308 subsonic, .260 subsonic and 6.8 subsonic route.
Also, for your review and consideration:
Safely Develop and Load Subsonic Ammunition "The loading of subsonic ammunition should not be undertaken lightly. Done incorrectly or by the incautious or inexperienced, it presents a significant risk of grievous bodily harm to the shooter."
The goal is to explain techniques used to safely develop and load subsonic ammunition without risking life and limb. The ultimate danger in subsonic loading is a phenomenon known as Secondary Explosive Effect (SEE). SEE can destroy the strongest rifle action and it can happen on the first shot or the tenth. In fact it is more likely to happen after the bore is dirty from the first few shots. SEE is the result of slow or incomplete ignition of small amounts of smokeless powder. The powder smolders and releases explosive gases which, when finally ignited, detonate in a high order explosion. The warning sign for imminent SEE is a hangfire or delayed ignition.There are a number of techniques that can be used to prevent or delay the onset of SEE. These involve specially prepared cases as well as bullets, in addition to selecting a suitable powder and primer. Lets begin with the easy stuff. All reduced velocity loads should start with a magnum primer. The hotter and longer duration flame ensures the small powder charge lying in the bottom of a large rifle case is properly ignited. Testing revealed that accuracy is increased 8% with magnum primers. Reloading manuals contain minimum powder charges for a reason. Going much below the minimum load with a slow burning rifle powder can trigger SEE. Subsonic loads use fast burning pistol powders, the faster the better. This ensures the powder is easy to ignite and will be totally consumed before the bullet leaves the muzzle. Not only is this safer but it is quieter as well. Quieter is always good when operating in the subsonic realm. A secondary consideration when choosing a powder is its bulk density. That is the amount of volume a given weight of powder will occupy in the case. Bulk densities are typically measured in grains per cubic inch; with the lower number meaning the powder is more voluminous. Fluffy (low bulk density) powders like Red Dot take up much more room in the case. Load density is safety in a subsonic load. It is suggested that loads never go below 30 percent load density (powder occupies 30 percent of the case volume) unless you want to dance with the devil and the deep blue SEE.
Load density can be measured by dropping a length of wood dowel into the loaded case. Mark the dowel where it meets the case mouth. Then pull the dowel out and compare it against the case. Keep notes on load densities for every powder and case combination so that safe loads can be identified at a glance before they are loaded. Don't go below 30% load density!
Powders suitable for subsonic loads include: N310, N312, Bullseye, Clays, Titewad, HP38 and Red Dot. There are other suitable powders available but these are the best to start out with. Red Dot is probably the best powder to work with because it gives the highest load densities. The Vihtavuori powders (N310 and N312) are particularly interesting because they burn very quickly and cleanly and they exhibit exceptionally stable performance over an extremely wide range of environmental temperatures.
Powder burn rates are important because the low pressures generated by subsonic loads are typically not sufficient to properly seal the case in the chamber. Faster powders create better sealing and less sooty blow-by on the outside of the case. Once the powder choice has been made, the next step is to select and prepare the bullets. Bullet choice for subsonic shooting is much more critical than for conventional ammunition. Low velocity greatly reduces the projectile's rotational rate (RPM) and thus stability. Fast twist barrels are essential to successful subsonic loads. In .30 calibre this means a 1:10 twist or faster. A 1:10 twist will stabilize a 220 grain round-nose bullet at 950 fps. Computer programs that calculate projectile stability are available free on the Internet. These calculators usually quote a Stability Factor (SF) of 1.3 for full stabilization in a conventional load. It has been found through testing that a SF in the range of 2.0 to 2.2 or greater is needed for a bullet to fully stabilize at subsonic velocity. This depends on how well the bullet is balanced with its center of mass. Lapua makes a special subsonic 200 grain .30 caliber bullet that is stable with a SF of only 1.36.
To prevent bullets sticking in a dirty bore, all conventional jacketed bullets used for subsonic loads must be lubricated. There are two primary methods of achieving proper lubrication. The traditional method is to dip the bullets in melted, refined animal fats (lard). The fat hardens as it cools, leaving a thin, slick surface on the bullet. The downside is this method is messy and slow. The modern method is to simply use moly coated bullets. Moly is easy to get and can be applied to bullets by the hundreds in only a few hours. Moly coated bullets are also available direct from the factory. Moly coated bullets were used exclusively in testing for this article and the author has never had a coated bullet stick. The same cannot be said for uncoated bullets. As a side note, cast lead bullets are inherently lubricated and do not need to be coated. One final note on bullets for subsonic loads. Never crimp and don't seat bullets into the lands. Bullets should be seated with lots of jump for safe operation. The most radical modification required for safe subsonic ammunition comes in the case preparation. To take advantage of the magnum primer, the flash-hole should be drilled out to 9/64 inch (3.5mm) for a large-rifle primer. The enlarged flash hole allows as much of the primer flash as possible to reach the powder. This is especially important in full sized rifle cases. It also helps to prevent primer setback due to the low operating pressure of these rounds. DO NOT use subsonic modified cases for full power ammunition! Now that all the components are gathered and properly prepared, we are ready to begin to develop ammunition. Unfortunately this is where things get difficult. There is almost no published subsonic load data anywhere. It is almost unheard of in any load manuals and it is fairly scarce on the Internet. A starting or reference point is needed to work from to avoid operating blind in the dark, which is not a good place to be when dealing with potentially explosive components. CE Harris developed a fairly well known reduced power load known as "The Load." Information on "The Load" can be found fairly easily in an Internet search. To throw the reader a bone, here are the basics. "The Load" can be used in any full sized rifle case without any modifications to the components. It consists of 13 grains of Red Dot (greater than 50 percent load density in .30-06 case) driving a lightweight bullet (125 grain in a .30 caliber) at medium velocity (approximately 1,600 fps). The smart and experienced reloader should be able to extrapolate a safe starting load for heavy bullets from The Load. Keep in mind it is better to start a bit fast and work the velocities down slowly remembering NEVER to go below the 30 percent load density rule (It really should be a Law!)When using a medium to small sized case, it is possible to compare internal volumes with other cases to find suitable starting data. For example the author discovered the .44 Magnum case (with a bullet seated) has almost the same internal volume as the 7.62x39mm case. All sorts of .44 Magnum load data exists for 180 to 220 grain bullets from which safe starting subsonic loads can be extrapolated. Once the first test loads are assembled, it is time to head to the range and see how they work. A chronograph is essential to developing safe subsonic loads. Don't even try it if you don't have access to one. The target velocity to work towards should be 50-100 fps less than the speed of sound or about 950 fps. This puts velocity below the transonic range where the supersonic crack begins to be generated. The sonic crack is not generated at exactly the speed of sound. The sound increases in volume across the transonic range starting about 92-93 percent of the speed of sound based upon research by Al Paulson. Also keep in mind that a sound suppressor (silencer) may create about 30 fps of freebore boost, which in turn argues for lowering projectile velocity an additional 30-50 fps. At about 50 fps above the speed of sound the sonic crack reaches maximum volume. During the initial testing period, it is important to start with a clean and lightly lubed bore to ensure bullets slip down the barrel easily. The bore should be lubed after every 2 or 3 shots to keep it clean and slippery. Velocities will vary somewhat due to the oil in the bore but at this point safety is more important than consistency. Make sure the bullet leaves the bore after every shot. Most of the time it is possible to hear the slow moving bullet hit the target but if need be physically check the bore. A stuck bullet will ruin your barrel and the day. The first range session should be all about finding a safe load that meets the 950 fps requirement. It is certainly possible to go much slower than this but the danger of triggering SEE does not warrant the slight reduction in muzzle signature.
Subsonics are very sensitive to barrel condition and fouling. Velocities can vary considerably depending on how clean the barrel is. Temperature can also have a great effect on subsonic muzzle velocity. Once a safe load or two in the desired velocity range has been found, a second range session can be used to test the effects of reducing the bore lubing frequency as well as the consistency and trajectory of the load. Subsonic loads require the shooter pay attention at all times. A stuck bullet is always possible, with predictable results. Always remember a hangfire or delayed ignition signals impending SEE. To easily distinguish modified cases (and subsonic ammunition) from conventional rounds, use a blue indelible felt marker to color either the case extractor groove or the case head. The blue case head (right) is more traditional and is still used by Lapua for their subsonic ammunition. The author prefers the blue extractor groove (below, right) because it is easier to see when handling ammunition and doesn't rub off as easily. Once you become comfortable loading and shooting subsonic ammunition you will find that they are a lot of fun to shoot. There is hardly any recoil and muzzle signature is reduced to a slight pop. Shooting without hearing protection is comfortable and it is even possible to hear the bullet hit the target with a loud "Thwack!"
Rules for the safe operation of subsonic loads:
1. Drill Flashole to 3.5mm (9/64") to allow all the primer flash to enter the case and ignite the powder completely.
2. Use Magnum Primers for maximum primer flash and better powder ignition.
3. Lube all bullets. Moly is good, animal fat is better.
4. Lubricate the bore regularily while shooting.
5. Never crimp bullets into cases. Never seat bullets "into the lands."
6. Try not to use powder charges of less than 40% load density.
7. If load density is less than 40%, use tamping or fillers to keep the powder at the bottom of the case.
8. Make sure the bullet exits the bore after each shot.
9. Use only the fastest burning pistol powders - N310, N312, Bullseye, Clays, Titewad, HP38, Red Dot.
10. Any sort of slow ignition or hangfire is a warning of iminent Secondary Explosive Effect (SEE).
Always mark subsonic cases so that they are NEVER USED FOR SUPERSONIC PRESSURES.
16" Krieger 1/10
220 Hornady RNSP
10.7 gr of Trail boss
1040 fps
mag primers, win cases
3/4-1" groups at 100
not temp sensitive or powder position sensitive
slightly louder than loads with Green dot or other pistol powders, but more reliable.
200 gr Lapua Subsonic, 8.2 gr Red Dot, WLRM, 2.20" O2H
950 fps @ 90F
200 gr Lapua Subsonic, 10.0 gr Trail Boss, WLRM, 2.20" O2H
967 fps @ 70F
Come-ups
100 yds, 4.2 mil
200 yds, 9.2 mil
280 yds, 14.2 mil
Remington M700, 16" 1/10", War Tech Tensioned Barrel System w/ST Black Star 8" installed, H&S 5R stock and bottom metal, Leupold MK4 1-piece base, Leupold MK4 1" Medium alloy rings, Bushnell 3200 10x40:
Case: Federal Gold Medal
Primer: CCI 200 Large Rifle
Powder: IMR Trail Boss
Bullet: Sierra 170gr (30-30) bullet .308 dia. #2010
Starting Load: 9.0gr (980 fps average)
Work Up: loaded to 9.8 (1017 fps average)
Accuracy Load: so far most producing Sub-MOA
Basic Dope:
0'd @ 50yd
75 - 2.25MOA
100 - 4.5MOA
125 - 7.0MOA
150 - 9.5MOA
Note: this is a fun target load that is less expensive and @ 200yds has been a killer on 8oz. water bottles. this is also a load that has been proven lethal to 102yds for the average Whitetail or rather large gray squirells that are considered armed and dangerous! Will update with more results with better weather conditions which will permit Chrony and groups, stay tuned.
1/10 twist, 18" Krieger
220 Hornady RNSP
Win Mag Primers
2.8"
10.5 Greendot
1 ragged hole at 100m
2" grp at 200m
Same as above w/10gr Trail boss
1" at 100
3.5" at 200
30 CAL Twist rate:
1/12: 180 grain and below for the SMK types designes (AMAXs, FMJ, anything with a pointed tip and boattail) 190's with a RN design
1/10: 200 and below for pointed designs, 220 for RN designs
1/8: 240 and below for pointed design, I don't know of a 30 cal round nose design greater than 220.
Using a 223 subsonic is no different that a .22 subsonic, just more expensive. Bullet weights are similar and the velocities are the same. Besides, to get sub 223 loads you have to do a lot of researching for the right load and spend an awfull lot of time prepping the rounds. For .22, just stop by walmart...
If you want to go after 223 subs, I used greendot with about 8 grains. That was back in 2000, now I'd try trailboss, SR 4759, or RE7.
For powder in a 308:
Pistol powders are more quiet (2-4dB which is barely audible to the ear). However, they have several drawbacks:
1. Extremely small case capacity which leads to significant velocity spreads due to position sensitivity. For example, above, I'm quoted with a load for greendot. While the accuracy was excellent, I had to make sure I did tilted the barrel up and tapped the rifle to seat the powder against the primer for every shot to get those groups.
2. They are very temp sensitive
3. A doubled charge (or even one that's just a few grains over) will quickly create a pressure spike and can lead to the case failing
For the bulkier powders (TB, 4759, RE7, Accurate 2250 ro somehting like that.. not sure but it's labeled as a bulky powder for low power loads) , just add a little water to the can to surpass the suppression level of the pistol powders. Click...wait...wait...wait...thump is what you get.
Trail Boss isn't the universal holy grail for subsonic rilfe loads but it's a great place to start. For 308s with barrels over 16", start around 10 grains. I haven't found enough evidence that there is a temp sensitivity, but there certainly isn't a case position sentisitivity. With the heavier 220-240 gr bullets, I've had a hard time getting them to 1050 with TB in my pistol. Consequently, I played around and found IMR SR 4759 and have been very happy with it from 5-65 deg.
Others are playing with H110 and CLAYS, but the same problems arise as with the pistol powders.
For primers, I always use mag primers, but they might not be necessary with Trail Boss or other bulky powders. I am convinced that they are the safest decision when using pistol or shotgun powders due to the small case capacity
Savage 10fp .308 1-10 twist factory 24" barrel
170 grain harnady fp
Federal brass full lenth sized
Winchester lr mag primers
9.5 grains of red dot
It's done a half inch so far at 100
308 Win. 26" bbl 1/11 twist, GAP Palma chamber.
Hornady 180 RN
Lapua brass
CCI BR2
10.2gr. Trailboss
2.650" COAL
1030fps @ 80*F
Hornady 180 RN
Lapua brass
CCI BR2
8.0gr. Titegroup
2.650" COAL
1040fps @ 80*F
thanks, but i can't take credit for it as not one is mine. they're everyone else's. on a snowday i figured i'd flip through the numerous .308 subsonic threads and pick some loads and tips to use for when the time is right.
from what i got from all of them is that trail boss seems to be the go to or most used, start around 11 / 11.5 which will probably go supersonic, then back it down from there. when your confident that it'll stay subsonic at different temps / weather conditions (within normal for your area) then you can stop so you don't end up with a stuck bullet.
my guess is i'll probably end up 10-10.5 gr of trail boss with a 180 RN when all is said and done, with a OAL that has some "jump" in it to the lands. since it's subsonic, all the gucci bullets BCs seems to not matter. since i like moly, it also appears i don't have to further lube anything.
i'm not going to mess with larger flashholes, but may entertain using magnum primers, no crimp on the bullets, and seperate bras for subsonic loads only.
also being new to the subsonic game, i don't think i'll get myself into any trouble with that combo, just wish winter would leave so i can start tinkering.
from what i got from all of them is that trail boss seems to be the go to or most used, start around 11 / 11.5 which will probably go supersonic, then back it down from there. when your confident that it'll stay subsonic at different temps / weather conditions (within normal for your area) then you can stop so you don't end up with a stuck bullet.
my guess is i'll probably end up 10-10.5 gr of trail boss with a 180 RN when all is said and done, with a OAL that has some "jump" in it to the lands. since it's subsonic, all the gucci bullets BCs seems to not matter. since i like moly, it also appears i don't have to further lube anything.
i'm not going to mess with larger flashholes, but may entertain using magnum primers, no crimp on the bullets, and seperate bras for subsonic loads only.
also being new to the subsonic game, i don't think i'll get myself into any trouble with that combo, just wish winter would leave so i can start tinkering.
It might have already been mentioned, but one thing I was taught for subsonic load development was to 1) "work down" your load ( say going from 12gr of PowderXX, to 11.8 etc. using a chronograph. 2) make sure prior shooting a selected load through your expensive suppressor to test the load with a cardboard target placed close in so one would be able to note gyroscopic stability in your projectile. If the hole is oblong, the projectile may be unstable, and could cause a baffle strike, and ruin your, day.
YMMV-FWIW
YMMV-FWIW
Top Predator,
Thanks so much for all this information. You've undoubtedly forgot more about sub-sonic loads than I'll ever know. I was aware of the SEE effect, but I didn't really understand how it occurred. One guy was trying to tell me that it was caused by the primer igniting too much powder all at once.....Apparently there is a lot more to this.
I've heard that some people fill part of the case with some other substance to reduce the powder capacity, thus reducing the chance of the SEE effect. I can't recall the exact composition of that other material.....Is that a good idea? My knowledge is really limited on sub-sonic loads.
Thanks so much for all this information. You've undoubtedly forgot more about sub-sonic loads than I'll ever know. I was aware of the SEE effect, but I didn't really understand how it occurred. One guy was trying to tell me that it was caused by the primer igniting too much powder all at once.....Apparently there is a lot more to this.
I've heard that some people fill part of the case with some other substance to reduce the powder capacity, thus reducing the chance of the SEE effect. I can't recall the exact composition of that other material.....Is that a good idea? My knowledge is really limited on sub-sonic loads.
The filler substance most commonly mentioned is Cream of Wheat. Also used for fire-forming new cases. Oatmeal, farina, grits, rice crispies, Cap'n Crunch; any 'cereal' that will confine the charge to a smaller space, but still will crumble to dust under pressure. I've also heard of tissue paper being used. Using a filler is better than risking SEE, but using a powder that fills enough of the case to avoid the risk altogether is an even better idea. And NEVER shoot any cartridge with an inert filler through any kind of muzzle device; brake, flash hider, or suppressor.
All the theories about SEE are just that, because no one can reliably replicate it, on demand, in the laboratory.
Another problem to be aware of with subsonics is that the charge weight is so light, you've got very little of margin of error between a normal load and a squib. And the odds of a squib increase dramatically with barrel length. The guys at Engel Ballistics Research have a lot of experience in that regard, and they caution against ever using subsonic ammo in a barrel longer than 20". This is why you have to keep track and make certain you see evidence of each round's impact. If you're not convinced, better check your bore before you send another one.
EDIT:
One more point. A sonic "boom" -- which is what the "crack" of a SS bullet really is -- is a very densely compacted region of air. It will bounce off everything it strikes as if it were a very dense rubber ball, like a superball. Which means SS crack echoes like a mutha. Unless you are shooting someplace as flat as the Mojave Desert, and there is NOTHING above ground level downrange from you (no trees, no fence posts, not even a target stand), if you are shooting suppressed (and your suppressor is worth a hoot) you WILL hear the echo of a SS bullet's crack. Even if you're wearing hearing protection (maybe not if it's cups AND plugs). Not recommended to be used as a gauge for load development, but if you can hear your SSS bullet as it travels downrange, it ain't SSS.
EDIT II:
I was only joshin' about the Cap'n Crunch.
All the theories about SEE are just that, because no one can reliably replicate it, on demand, in the laboratory.
Another problem to be aware of with subsonics is that the charge weight is so light, you've got very little of margin of error between a normal load and a squib. And the odds of a squib increase dramatically with barrel length. The guys at Engel Ballistics Research have a lot of experience in that regard, and they caution against ever using subsonic ammo in a barrel longer than 20". This is why you have to keep track and make certain you see evidence of each round's impact. If you're not convinced, better check your bore before you send another one.
EDIT:
One more point. A sonic "boom" -- which is what the "crack" of a SS bullet really is -- is a very densely compacted region of air. It will bounce off everything it strikes as if it were a very dense rubber ball, like a superball. Which means SS crack echoes like a mutha. Unless you are shooting someplace as flat as the Mojave Desert, and there is NOTHING above ground level downrange from you (no trees, no fence posts, not even a target stand), if you are shooting suppressed (and your suppressor is worth a hoot) you WILL hear the echo of a SS bullet's crack. Even if you're wearing hearing protection (maybe not if it's cups AND plugs). Not recommended to be used as a gauge for load development, but if you can hear your SSS bullet as it travels downrange, it ain't SSS.
EDIT II:
I was only joshin' about the Cap'n Crunch.
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I tried 220gr round nose bullets in my savage 1:10 twist and didn't like it. They all hit nose forward, but no matter what I did I couldn't get accuracy better than 4 moa or so.
I settled on trail boss and 208amax's. They work great but I still couldn't get them to print better than 2moa
However, I decided that's more than enough for their purpose and the effective range of subsonics.
As with what others have said, the main issue is vertical stringing. Horizontally, it can be better than a a half minute load, but vertical stringing is what makes it 2moa.
I settled on trail boss and 208amax's. They work great but I still couldn't get them to print better than 2moa
However, I decided that's more than enough for their purpose and the effective range of subsonics.
As with what others have said, the main issue is vertical stringing. Horizontally, it can be better than a a half minute load, but vertical stringing is what makes it 2moa.
Try loading seating them backwards, point in, base out. Seriously. The CG on a streamlined bullet is on the wrong end for optimal stability. Firing them bass-ackwards makes them easier to stabilize. Free bonus, with subsonics, a blunt meplat tends to have better terminal effects than a pointy one. Somewhere on the Hide, there's a thread started by a guy who was demonstrating that on a pot roast. The aerodynamic efficiency sucks, but if you were planning on 400 yard precision fire, you wouldn't be shooting subsonics anyway.
EDIT:
I found the post. It wasn't pot roast, it was a deer carcass. And it wasn't a test of backwards bullets, but it was comparing terminal effects of a round nose bullet vs. high-ogive. And the round nose won, which would tend to support a theory that, at SSS velocities, largely lacking hydrostatic shock effect, the blunter meplat does more tissue damage.
EDIT:
I found the post. It wasn't pot roast, it was a deer carcass. And it wasn't a test of backwards bullets, but it was comparing terminal effects of a round nose bullet vs. high-ogive. And the round nose won, which would tend to support a theory that, at SSS velocities, largely lacking hydrostatic shock effect, the blunter meplat does more tissue damage.
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Wow that was a helluva informative post. I don’t have any Trailboss powder but have endless supply of Titegroup and I’m gonna give it a try. Thanks for the post.
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