Stabilizing the .308 220 grain

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Minuteman
Jul 30, 2014
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#1
Hey guys Im new to the hide but have always seeked this place as a valuable tool for learning from the most experienced shooters around. I tried looking up this info before posting but I never could get a defined answer.

I have a Reminton 5r Milspec with a 11.25 twist rate and would like to know your thoughts on stabilzing a subsonic 220 gr SMK through it. I also have a Remington 1-10 twist accsd .308 that I know will stabilize it, but it is down due to baffle strikes since remington cant thread there barrels straight. While that is being fixed im hoping to run my can on my 5r so I can develop a subsonic 220 gr load.

Please let me know if you have any suggestions.

Thanks.
 
#2
No way will you get that bullet to stabilize in a 11 twist, a 220gr round nose won't even stabilize in a 1:11. 220 SMK is also too long for a 1:10 in most conditions. For subs in a 1:11 180gr round nose or flat point is about the best you're going to get stable. 1:8 and 1:7 is recommended for what you're trying to do.
 
#3
Ive never seen a factory bolt gun with a 1:8 -1:7 twist. Im guessing I would have to go aftermarket for that.

Im new to the whole suppressed subsonic market, and just started reloading so im trying to gain all the knowledge I can on the subject.

If I were to go replace the barrel on either rifle, I think I would like a bartlein barrel with a transitional twist. Maybe a 1:10 at the breech and a 1:7 at the muzzle! Im not even sure if that would work but i like the custom aspect of it. In the end i just want a rifle that can deliver 220gr SMK or gamekings at sub moa.
 
#4
At subsonic speeds the BC of the SMK really doesn't do much for you. I'd stick with the 1:10 and run the 220gr round nose from Hornady or Sierra.

If you are dead set shooting that bullet I'd suggest getting the 300BLK handy rifle, it has a fast twist for the heavy ones.
 
#5
redneckbmxer24 said:
At subsonic speeds the BC of the SMK really doesn't do much for you. I'd stick with the 1:10 and run the 220gr round nose from Hornady or Sierra.

If you are dead set shooting that bullet I'd suggest getting the 300BLK handy rifle, it has a fast twist for the heavy ones.
Click to expand...

Thanks for the input sir. Im not dead set on the 220gr, I just have a problem with wanting the biggest and baddest. I figured I would want the heaviest bullet possible so It wouldnt reach supersonic. I Looked into the 300blk but It seems to shine when used in the ar15 platform. So now im attempting to just use one of my Rem 700's to fill the role of a subsonic Hog Hammer! I wont lie though....the aac micro 7 has caught my eye :)
 
#6
When you're talking subsonic velocities a 220gr smacking something is a 220gr. The difference between the SMK and the round nose though is the round nose is much shorter and will stabilize in a 1:10 twist. Next time you see the 220gr round nose from Hornady or Sierra go in stock I'd buy them up. Stock yourself up too because they've only been making them about once a year.
 
#7
What redneck said. I tried the 220gr Sierra ProHunter round nose in my 26" 11 twist TRG and they were tumbling to the target at 100 yards. No way I would try them with my can on it. I did work up a fairly accurate load using 170gr Sierra ProHunter round nose. The 220gr work great in my 16" 7 twist AAC Blackout AR.

Good luck
 
#8
redneckbmxer24 said:
When you're talking subsonic velocities a 220gr smacking something is a 220gr. The difference between the SMK and the round nose though is the round nose is much shorter and will stabilize in a 1:10 twist. Next time you see the 220gr round nose from Hornady or Sierra go in stock I'd buy them up. Stock yourself up too because they've only been making them about once a year.
Click to expand...

geez its hard enough finding powder for the dang thing, and now I have to wait for an elusive bullet to come out :(.........sadness
 
#9
Fixr said:
What redneck said. I tried the 220gr Sierra ProHunter round nose in my 26" 11 twist TRG and they were tumbling to the target at 100 yards. No way I would try them with my can on it. I did work up a fairly accurate load using 170gr Sierra ProHunter round nose. The 220gr work great in my 16" 7 twist AAC Blackout AR.

Good luck
Click to expand...

Thanks Fixr, the more info the better!
 
#10
For S&G I worked up a subsonic load using 220gr RN I had on hand. Rifle was 1/12 twist 308. At 1050 fps they were wobbling into the target at 100 yards, with about 2 moa accuracy. The R5 with 1/11.25 twist would be a little more stable than my 1/12, but you would need to try it out and see if it worked or not.



 
#11
MontanaMarine said:
For S&G I worked up a subsonic load using 220gr RN I had on hand. Rifle was 1/12 twist 308. At 1050 fps they were wobbling into the target at 100 yards, with about 2 moa accuracy. The R5 with 1/11.25 twist would be a little more stable than my 1/12, but you would need to try it out and see if it worked or not.



Click to expand...

Thanks for the photo. Im noticing a common factor is that everyone is using round nose and ive already purchased 220gr sierra smk's. I hate to just throw them away.
 
#12
220g SMK's are BARELY stable in the 10 twist subsonic according to JBM Ballistics stability calculator. With that said I have shot probably 250-300 out of my 10 twist AAC-SD and they were all stable. I would NEVER try them out of the 11.25 twist 5r barrel.

I always use the JBM stability calculator before buying a new bullet to try subsonic.

Hell you can download the 147g/150g FMJBT mil pulls to subsonic in a bolt gun very easily and have a mouse fart load.

I think one of the BEST bullets for subsonic is the couple of 180g round nose flat base bullets that are crazy hard to find. The flat base supposedly helps the bullets fly better subsonic than the boat tails do.
 
#14
The stability of the bullet is not quite as straight forward as it looks at first glance. I've plotted the stability domain to answer the question originally posted. The stability of the bullet is dependent on several things; and as such it varies even if we assume the muzzle velocity is temperature insensitive and is always 1050 fps.

Below is a plot of the stability factor for a 220gr MK at 1050 fps and given a twist rate of 1:11.25 as conditions vary from 0 deg F to 100 deg F:

220 MK stability (1125).jpg

The gray area is the stability factor. The blue line is at Sg = 1.4 which is the minimum we'd like to see for a properly stabilized bullet (ref. Bryan Litz). The red line is Sg =1 which is the transition between stability and instability. If you are at sea level your stability curve is the bottom black line, but if you're at a higher elevation your stability line is closer to the upper black line. I set the upper black line at a pressure that corresponds to about 10,000 feet above sea level. Notice that the bullet in certain conditions is below the red line and is completely unstable! In other conditions the bullet is marginally stable, and it's only at very high altitudes that the bullet is properly stable.

Now here is the same plot with a 1:10 twist barrel:
220 MK stability (10).jpg

There's a big difference! I hope this helps you understand what's going on. Cheers.
 
#15
Go with the hornady 308 160gr FTX shot them out to 600yds the other day and that pushing it. 500yd I was hitting the gong with a %65 hit rate.I have a 1-12 twist and works well. 9.7gr of trailboss at 1040fps
 
#16
If you want to go subsonic screw the 308, it has too big of a case to give good consistency. If you just want to run 220gr in your 308 you still need a faster twist rate unless you can get the speed up near 3000fps or so. They're just too long to stabilize well in an 11 plus twist. I can't imagine shooting them out of a 1-10 twist. On the other hand.....remington does make the 300 blackout with a 1-7 twist and even then they were tumbling 220gr noslers and the 220gr matchkings were not hitting pointy end straight every time. This was at 1060fps.

Frank
 
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#17
bmacconaghy said:
The stability of the bullet is not quite as straight forward as it looks at first glance. I've plotted the stability domain to answer the question originally posted. The stability of the bullet is dependent on several things; and as such it varies even if we assume the muzzle velocity is temperature insensitive and is always 1050 fps.

Below is a plot of the stability factor for a 220gr MK at 1050 fps and given a twist rate of 1:11.25 as conditions vary from 0 deg F to 100 deg F:

View attachment 44828

The gray area is the stability factor. The blue line is at Sg = 1.4 which is the minimum we'd like to see for a properly stabilized bullet (ref. Bryan Litz). The red line is Sg =1 which is the transition between stability and instability. If you are at sea level your stability curve is the bottom black line, but if you're at a higher elevation your stability line is closer to the upper black line. I set the upper black line at a pressure that corresponds to about 10,000 feet above sea level. Notice that the bullet in certain conditions is below the red line and is completely unstable! In other conditions the bullet is marginally stable, and it's only at very high altitudes that the bullet is properly stable.

Now here is the same plot with a 1:10 twist barrel:
View attachment 44830

There's a big difference! I hope this helps you understand what's going on. Cheers.
Click to expand...
I'm working with the 220 smks as well, gas gun, 1:9.5 16". I understand it's a long shot but if I can get it up to 2200 fps or so, could it work?

Also, can you help me understand how temperature is the primary variable in determining stability in the chart you provided? Is it just air density?
 
#18
dmike said:
I'm working with the 220 smks as well, gas gun, 1:9.5 16". I understand it's a long shot but if I can get it up to 2200 fps or so, could it work?

Also, can you help me understand how temperature is the primary variable in determining stability in the chart you provided? Is it just air density?
Click to expand...

It's not the primary variable; temperature is just the most likely to change. I made the graph that way, because it just seemed the most reasonable way to display the data. I mean, it's not like you're likely to change elevation by several thousand feet with the same temperature, right? You're right to say that the temperature relates to air density, but it's just one of the variables.

What powder were you planning to use for your gas gun? I'll do some calculations tomorrow to see where it lies. cheers.
 
#20
I agree that the RN 220 bullets would be a much better choice for a 11.25 twist barrel. Here's the stability region for that;
220 RN stability (1125).jpg

They're actually kind of ideal.



MontanaMarine said:
For S&G I worked up a subsonic load using 220gr RN I had on hand. Rifle was 1/12 twist 308. At 1050 fps they were wobbling into the target at 100 yards, with about 2 moa accuracy. The R5 with 1/11.25 twist would be a little more stable than my 1/12, but you would need to try it out and see if it worked or not.



Click to expand...
 
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#22
bmacconaghy said:
A 16" 308 should be able to push a 220 MK to about 2200 fps. And with a 9.5 twist rate the stability region looks like this:

View attachment 44910

Looks like you're in good shape in any altitude and temperature.
Click to expand...

So I got the 220 SMKs to about 2200 with the N150 (prochrono was all over the place lol). Got the COAL out to 2.82 with the dpms mag. I am stopping at 39.9 due to pressure signs, and it never stabilized in my 9.5 twist. At 400 yards the spread was about 10 MOA.

The good news is that my 208 AMAXs arrived just as I was headed to the range so I loaded up 3 hasty ones. No pressure signs at 2175ish and all 3 hit the 18" plate at 400 so I'm sure they were flying right. I'll see if I can get them to 2250. I'll do a more detailed workup on Sunday and post results.

Any 300WMers in VA/MD need my leftover 220s?
 
#23
The question of bullet stability is not the same thing as accuracy of the load. Did the bullets go straight through the paper? Did they go sideways through the paper? If they punched straight through then they are stable. If you see large oval shaped or bullet profile shaped holes then they are unstable. I think others can chime in their experience, but my experience is that the maximum pressure load is rarely the most accurate. I think you are dealing with an inaccuracy problem not a stability problem. I hope the other bullets work out better for you.



dmike said:
So I got the 220 SMKs to about 2200 with the N150 (prochrono was all over the place lol). Got the COAL out to 2.82 with the dpms mag. I am stopping at 39.9 due to pressure signs, and it never stabilized in my 9.5 twist. At 400 yards the spread was about 10 MOA.

The good news is that my 208 AMAXs arrived just as I was headed to the range so I loaded up 3 hasty ones. No pressure signs at 2175ish and all 3 hit the 18" plate at 400 so I'm sure they were flying right. I'll see if I can get them to 2250. I'll do a more detailed workup on Sunday and post results.

Any 300WMers in VA/MD need my leftover 220s?
Click to expand...
 
#24
bmacconaghy said:
The question of bullet stability is not the same thing as accuracy of the load. Did the bullets go straight through the paper? Did they go sideways through the paper? If they punched straight through then they are stable. If you see large oval shaped or bullet profile shaped holes then they are unstable.
Click to expand...

You make an important distinction between the two. Although, in my limited experience, there is a correlation there. it would be difficult to get an unstable bullet to perform consistently (accurately) at range. Similarly, a stable bullet would exhibit some degree of consistency/accuracy...not necessarily sub-moa but hopefully better than 10 MOA.

I can't speak to the bullets' orientation when they impacted steel at 400yds. I can tell you that in my 9.5 twist gas gun the 220s going 2200fps hit 400yd steel (18") less than 10% of the time, and POI was up to 3' off POA in all directions; 1 o'clock, 8 o'clock, 5 o'clock etc. That led me to believe the bullets were already tumbling early in their flight. The test 208's all hit the steel, which would be tough to do if they were completely unstable. I'm still in load dev but I have 208 AMAXs around 1.5 MOA (at 200) with no keyholes, around 2175fps. With the 220s I wouldn't even be able to get them on the paper.

Idiot warning: not proud of the following but I have to tell the truth...
The piston gun was at the smiths for a while, they worked on it and shot it some to confirm accuracy was at least moa. I got it back and just shot it. Once I got to 200 rds (plus whatever the smith did) and the chamber started looking dirty I took it apart this weekend and found the op rod was bent. It was still cycling on the last round fired, a Lapua D46 going 2424. I have no idea when the rod bent. It could have been when I had mild pressure signs with the 220s (mild cratering/wipe/ejector marks etc). gas port was on lowest setting (suppressor setting). New rod is in the mail today and I'll pay closer attention during load dev, taking it out for inspection between recipes.

Now for the strangest part of all.

I had 40 or so 220s left, no hope of shooting them in the 9.5 twist and no other rifle that could use them.

I happened to copper clean my 26" 1:12 700 SPS Varmint last week and I wanted to copper foul the barrel Sunday. I figured the massive bearing surface on the 220s would shed more copper per shot than anything else I had, and they were essentially useless to me, so I decided to load up 10 of them to copper up my barrel. I took advantage of the Remington's endless freebore and loaded them long at 2.976, still about 30 thou off the lands.

I expected them to shoot even worse than they did in the 9.5 twist, which as stated above was minute of barn. I guessed 11 MOA elevation at 400yds. Expecting to see a big dirt splash several feet from POA, I hit steel. 6 out of 7. So I went to paper at 400 to print a group with the last 3 and they were just over MOA, no keyholes. MV was around 2360 with no pressure signs.

I know barrel twist is not always an exact science, but I did not expect my 1:12 to stabilize 220 SMKs.
 
#25
I shot some 220 SMKs in my 1/12 308 with consistent sub-moa accuracy. I was scooting them along at about 2540 fps via moly, and RL-17. I did some plinking with them out at a mile, and they seemed pretty consistent even way out there, enough so that I believe they remained stable in the transonic speeds.
 
#26
I'm glad to see that the 208's were working for you. The 208's are longer that than the 220's (1.340 for the 208's and 1.292 for the 220's), so the 208's are actually less stable than the 220's are given the same twist and MV that we have in this case. I suspect that we are not looking as a static bullet stability problem in this case.


dmike said:
You make an important distinction between the two. Although, in my limited experience, there is a correlation there. it would be difficult to get an unstable bullet to perform consistently (accurately) at range. Similarly, a stable bullet would exhibit some degree of consistency/accuracy...not necessarily sub-moa but hopefully better than 10 MOA.

I can't speak to the bullets' orientation when they impacted steel at 400yds. I can tell you that in my 9.5 twist gas gun the 220s going 2200fps hit 400yd steel (18") less than 10% of the time, and POI was up to 3' off POA in all directions; 1 o'clock, 8 o'clock, 5 o'clock etc. That led me to believe the bullets were already tumbling early in their flight. The test 208's all hit the steel, which would be tough to do if they were completely unstable. I'm still in load dev but I have 208 AMAXs around 1.5 MOA (at 200) with no keyholes, around 2175fps. With the 220s I wouldn't even be able to get them on the paper.

Idiot warning: not proud of the following but I have to tell the truth...
The piston gun was at the smiths for a while, they worked on it and shot it some to confirm accuracy was at least moa. I got it back and just shot it. Once I got to 200 rds (plus whatever the smith did) and the chamber started looking dirty I took it apart this weekend and found the op rod was bent. It was still cycling on the last round fired, a Lapua D46 going 2424. I have no idea when the rod bent. It could have been when I had mild pressure signs with the 220s (mild cratering/wipe/ejector marks etc). gas port was on lowest setting (suppressor setting). New rod is in the mail today and I'll pay closer attention during load dev, taking it out for inspection between recipes.

Now for the strangest part of all.

I had 40 or so 220s left, no hope of shooting them in the 9.5 twist and no other rifle that could use them.

I happened to copper clean my 26" 1:12 700 SPS Varmint last week and I wanted to copper foul the barrel Sunday. I figured the massive bearing surface on the 220s would shed more copper per shot than anything else I had, and they were essentially useless to me, so I decided to load up 10 of them to copper up my barrel. I took advantage of the Remington's endless freebore and loaded them long at 2.976, still about 30 thou off the lands.

I expected them to shoot even worse than they did in the 9.5 twist, which as stated above was minute of barn. I guessed 11 MOA elevation at 400yds. Expecting to see a big dirt splash several feet from POA, I hit steel. 6 out of 7. So I went to paper at 400 to print a group with the last 3 and they were just over MOA, no keyholes. MV was around 2360 with no pressure signs.

I know barrel twist is not always an exact science, but I did not expect my 1:12 to stabilize 220 SMKs.
Click to expand...
 
#30
I also use the 200 grain round noise for my sub loads so dont think your stuck to just useing 220's. Im also useing trailboss powder. Been stable to 200 yards. But its got a hell of a drop out there ;)

Eta. Same gun as OP
 
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#31
Pinecone said:
Find someone who is shooting .300 Blackout and sell them to them.

How many do you have?
Click to expand...
I have 100 220gr SMK's....I found a heck of a deal for 500 blemished 175gr SMK for $100 so I loaded some of those up for subsonic rounds.

I am restricted to Magazine length for my bolt guns so I loaded 15 rnds up last night at 2.300 using graduated loads of trailboss. 3 rounds at 12gr, 11.5, 11, 10.5 and 10 for a quick velocity check. I know I need to be around 1050fps and hope to check this weekend. My 1:10 twist AACSD is at the gunsmith right now being rethreaded due to a horrific factory thread job. I believe I will try the 220's in it. Probably Load up 3 rounds with 12gr of trail boss just to see if it can stabilize them.

Do you have to shoot 100yds to obtain a key hole? or will 50 yds produce a key hole if the round is not stable.
 
#35
XTR said:
JBM - Calculations - Stability

^^

JBM Stability Calculator. It just might be handy for you.

Using 1.497 for the length on the 220SMK and assuming 1100FPS you need at least a 1:11, and that's iffy, a 1:10 will do the job
Click to expand...

thanks! I do have a 1:10 aacsd and plan on using the 220gr. So whats the thought process here......larger grain bullet so you can use more powder or smaller grain bullet like 175 and use less powder....any round can become subsonic with correct amount of trail boss, but is there a benefit to going with the heavier 220gr?
 
#36
If the MVs are all equal the heavier bullet gets to the ranges that you can shoot subsonic with more energy and less drop. Remember, you are shooting at 22LR velocities here.


Unless you've ever shot a 45-70 with black powder and 405 grain bullets you probably have no concept of the drop out to 200 yards (can you say three and a half feet from a 50 yard zero! Compare that to the average 3" from 100 to 200 for a 308.) and the heavier bullets launched at the same velocity have better ballistics. With a 220 launched at 1100FPS you are still talking about close to a mil of drop per 25 yards past 100 out to 200. Seriously, 6 inches per 25 yards. If you are going to hit something other than paper with a bullet moving that slow hit it with something heavy.
 
#37
XTR said:
If the MVs are all equal the heavier bullet gets to the ranges that you can shoot subsonic with more energy and less drop. Remember, you are shooting at 22LR velocities here.


Unless you've ever shot a 45-70 with black powder and 405 grain bullets you probably have no concept of the drop out to 200 yards (can you say three and a half feet from a 50 yard zero! Compare that to the average 3" from 100 to 200 for a 308.) and the heavier bullets launched at the same velocity have better ballistics. With a 220 launched at 1100FPS you are still talking about close to a mil of drop per 25 yards past 100 out to 200. Seriously, 6 inches per 25 yards. If you are going to hit something other than paper with a bullet moving that slow hit it with something heavy.
Click to expand...

Thats crazy. Thanks for that info. Very cool stuff
 
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