Subsonic accuracy

[matthias]

I have been working very hard with 300 blackout savage bolt gun over the last year to wring all the accuracy I can out of* this little cartridge. I have had decent luck with supersonic loads averaging between .25- .35 for five shots when using high end bullets and .3-.4 with standard off the shelf bullets. Bullet weight were from 110-185 grains
My issue is now I put a new barrel on with a faster twist to go subsonic and I am looking for advise on reaching a comparable level of accuracy with subsonic loads using heavy bullets 175-240 grains . So far not to much luck. Things I have tried are giving me around 1 inch groups the best being just a bit under .75
This is not about what I will use it for or why I want to get groups smaller . It's about making a rifle do what I want it to. Goal is to get it under .5 groups

Old barrel 1-10 16 inch long no taper 11* crown
New barrel 1-8 22 inch long no taper 90* crown

Using the same brass , Forster dies , and I have several pounds of different powders to try. Any suggestions for heavier bullet sub loads? Thanks for any help

 

[SUIScide]

I'd sure be happy if I could get a .75" group with subsonics! The good thing is since you have a bolt gun you can try other fast powders and aren't stuck with 1680.

 

[WRH51]

1" groups at what yardage? 100? If so that sounds pretty dang good to me for subsonic from what little I know. I am interested to see other comments on this and know what others have been able to accomplish on bolt gun and AR platforms.

 

[SUIScide]

Yeah, it sounds like Matthias should be teach us, not asking for help. I loaded some subsonic 22 hornets with Universal Clays if I remember correctly that were real consistent. Powder, primer, projectile, and seating depth how many combinations could there be;-)

 

[sic65stang]

What range? If 100 you are doing EXTREMELY well for subsonic

 

[matthias]

I am going to head to the range Friday and shoot the latest loads and let you know how it goes. Going to put bullets into the rifling and see if that will help. Later

 

[reeljob]

1" @ 100 is a good load for subs. You will drive yourself crazy chasing bugholes at that range. N110 seems to be my best powder that I run with 220 SMKs in the 1000 fps range. I did shot a sub moa group @ 100 a few days ago with 180 Hornady RN at 987 fps but the stars must have been lined up that day since it happend only once. From my expierence sub loading is a diffrent beast and consistancy in your process is critical. Sounds like you are on the right road though.

 

[pinsandpitons]

My .02 would be search out some short fat bullets. Don't run the SMKs or similar. Since they're moving slow, and won't go transonic, the more like a cylinder they are, the better they will stabilize (even in a faster twist) . Run a bullet stability tool and I think you'll see that a long slow bullet is bad. Even with a 1-8. Heavy is good, but you need it to be compact to be stable at the low RPMs of subsonic. Reeljobs results above point to that issue I think. Having said all this, you're clearly doing most everything right. My .308 sub load is 170gr FBRN over 10.0gr trailboss. With a lee factory crimp on the cannelure, it'll shoot .75" consistently if I dope the wind right. Have fun! BTW, 200yd steel with suppressed subs is my new favorite!

 

[bunsen27]

As others have said I believe you are quite a bit ahead of the curve with the accuracy of your subsonic loads.

http://bulletin.accurateshooter.com/2012/05/savage-cancels-300-aac-blackout-carbine-project/


I'm just starting up load development for my CVA Apex and will keep an eye int his thread.

 

[matthias]

I wonder if a wad cutter would work? Maybe something like the woodleigh hydrostatics line. Some Barnes bullets and my lathe might be in order.

I did go to the range Friday and sucked it up! Best was just over an inch worst was over two. With the blackout. The 458socom did better right at the .75 group average with the best just under half inch. Got to love 500 grain bullets

 

[pinsandpitons]

I think a real wadcutter would have some problems, but in my mind the perfect sub bullet would be like a Tylenol. round-ish on the ends to help with aerodynamics, but squat. That sucks that the blackout isn't performing better. What powder(s) have you tried?

 

[Michael Courtney]

You might try the Lehigh Defense ME 200. This bullet actually expands and is machined from copper to a very good tolerance level. We've never pushed the accuracy issue, but its weight, length, and geometry suggest it is stable (stabilized for us in a 1 in 10" twist at higher altitudes, 25 in Hg). The dimensional tolerances suggest a lot of accuracy potential.

 

[pinsandpitons]

What is the length?

 

[country888]

Any reason you went with a 22" barrel for subs? Who is the barrel maker?

 

[matthias]

I have seen the lehigh defense bullets and they are interesting. I have some lead bullets I am going to try. Then I am all out of ideas.

The barrel is longer to test out a theory that velocity can be controlled better with a longer barrel and higher charges. The idea is the powder is completely burned and the bullet is slowed by the longer time in the barrel. May be total crap and this thing might get cut to sixteen and one quarter . Just messing around.

 

[tctlrld]

Tag for info as I'm starting to assemble a 300 BLK bolt gun.

 

[Michael Courtney]

What is the length?

1.520" per http://lehighdefense.mybigcommerce.com/308-maximum-expansion-200-gr-subsonic-bullet/

 

[pinsandpitons]

What powders have you tried? I've been told low volume vs case capacity is always going to be inconsistent. That's why I am using trailboss in my sub loads. So far I've gotten great results, but I don't really know which of the details of my load are most critical for that. The one thing that tightened up my groups from about 1.5moa to .75 was the crimp, but that was the first thing I tried so......

Not trying to be a pest or sound like an expert (very much not!), just interested in the topic and what ends up working for you.

 

[matthias]

Lil gun, h110, 1680, 2400, bullseye. Trailboss is an interesting choice. What are your velocities ? Bullet choice? Platform?

 

[josephberry]

In my bolt, 10.8 grains of 1680 with the Hdy 225 match gives me MOA, (most of the time). It also cycles well in my AR.

 

[country888]

That is interesting Matthias, I havnt heard that but maybe worth trying. I have heard some people using Trail Boss. I want to give it a try even though I know it wont cycle a AR. A friend was using it with light 95gn and 110gn bullets for subs. He said they are very quiet from a Encore.

 

[pinsandpitons]

Lil gun, h110, 1680, 2400, bullseye. Trailboss is an interesting choice. What are your velocities ? Bullet choice? Platform?

.308 Win in Remington 700, 22" 5R barrel, suppressed with YHM Phantom QD
1020fps
170gr flat base round nose hunting bullets (pulled, no marks, cheep, .98" long)
10.0gr Trailboss
2.470 col with Lee factory crimp applied at cannelure
Fed brass
cci 200

I've never tried any other components so I may have just gotten lucky, but I did play with COL and charge weight a bit. It's not a full case by any stretch, but about 1/2 full, and with the deep seating, does a good job (I think) of keeping the ignition fairly consistent. I think in a .300 BLKout it would be very near a full case.

 

[SUIScide]

You may also looking for 300 whisper silhouette loads. The silhouette guys were shooting subsonic single shot pistols in this caliber way back in the stone age

 

[Retooferab]

This was shot out of my AR15 using N110. I would think with a bolt gun you could use faster powders. I have shot several groups like this using both 220 smk and 208 amaxes.

 

[pinsandpitons]

Ok, not trying to be a dick.... AR15? 220smk? You mean AR10 (or similar) right? Also, those holes look like .22 cal. Am I high?

I would like to hear your formula for subsonics out of your AR15 that cycle and shoot like that (if that's what you're showing).

 

[Retooferab]

300 whisper SBR 10.5" Shilen match barrel 1-8 twist. Thunderbeast 30P-1.
8.6 grains N110, 220 smk, Rem 7.5, LC formed brass. 2.09oal 1000 fps
8.0 grains N110, 208 Amax, Rem 7.5, LC formed brass. 2.17oal 1000 fps
Best accuracy with sub sonics is going to be between 980- 1000 fps. Any faster and you're up in the trans sonic range and has an effect on accuracy.

AR15

 

[Retooferab]

Also a faster twist with heavier bullets would help accuracy. AAC has now gone with 1-7 twist with 300 Blackout.
I have been playing with oal on these to tighten the groups up. It hasn't made much difference.

 

[Retooferab]

My .02 would be search out some short fat bullets. Don't run the SMKs or similar. Since they're moving slow, and won't go transonic, the more like a cylinder they are, the better they will stabilize (even in a faster twist) . Run a bullet stability tool and I think you'll see that a long slow bullet is bad. Even with a 1-8. Heavy is good, but you need it to be compact to be stable at the low RPMs of subsonic. Reeljobs results above point to that issue I think. Having said all this, you're clearly doing most everything right. My .308 sub load is 170gr FBRN over 10.0gr trailboss. With a lee factory crimp on the cannelure, it'll shoot .75" consistently if I dope the wind right. Have fun! BTW, 200yd steel with suppressed subs is my new favorite!

I agree with your theory on bullet shape. I just haven't found anything economical to use.

 

[Retooferab]

You might try the Lehigh Defense ME 200. This bullet actually expands and is machined from copper to a very good tolerance level. We've never pushed the accuracy issue, but its weight, length, and geometry suggest it is stable (stabilized for us in a 1 in 10" twist at higher altitudes, 25 in Hg). The dimensional tolerances suggest a lot of accuracy potential.

These bullets are accurate. I haven't shot them for groups. But I have shot a couple just to make sure they were close to my zero for other loads. Both shots were touching each other at 100 yards. I killed a small buck with one. Looked like it was shot with 300 mag instead of 300 Whisper.

 

[SUIScide]

I wonder if a wad cutter would work? Maybe something like the woodleigh hydrostatics line. Some Barnes bullets and my lathe might be in order.

I did go to the range Friday and sucked it up! Best was just over an inch worst was over two. With the blackout. The 458socom did better right at the .75 group average with the best just under half inch. Got to love 500 grain bullets

NOE makes a mold for a 250 grain cast boolit that may be as close to a wad utter as you can find w/o having a custom mold cut. I have some and what I've shot have been okay but I haven't worked up for good accuracy.
Also I don't think trail boss would be good in a blackout (well maybe with light bullets, like a subsonic Speer 130 grain HP?) cause I don't think you could stuff enough in a case. A 223 case would maybe hold ten grains of it filled to the mouth and a blackout with a 200+ grain bullet four grains maybe five. Just what I'm thinking I haven't tried it. I do load four grains of trail boss under a 55 grain bullet for subsonic 223 loads. That charge fills an estimated 40% of the case

 

[MarinePMI]

Perhaps this is a stupid question, but have you played around with your shooting position? It's been quite a few years since I played around with a .300 Whisper in a bolt gun, but I seem to recall that in order to get down to .5 moa, I had to be extremely cognizant of barrel time, bag position and how much pressure I leaned into the stock.

I may be totally off and have just imagined it, but it seemed to me that due to the sub-sonic nature of the round and the relatively heavy bullets, barrel time (and sensitivities to all the moving parts during ignition) played a huge role in accuracy. Far more so than something that was achieving 2700fps in the same barrel length and shorter time. This was a 23" HB, 1-7 twist .300 Whisper barrel.

Just a thought to throw out there....

 

[Bugholes]

1/2" groups with a good bolt gun in 300BLK are possible, i get many groups that are tiny then often manage a flyer- I think small discrepancies in your ammo will make larger discrepancies on the target. I quit chasing the elusive bughole load and became satisfied with a consistant .75MOA load. When doing load development you will see lots of elevation variances as you get a little faster or slower, controlling your ES should benefit here. I have an ES of around 20 (cant remember) which when you think percentage-wise is quite high. Imaging an ES of 60-70 in a 300FPS load...
I tried Trailboss in the sub 308 with 155s, accuracy was outstanding. Havent tried it in the BLK as load density would likely be too high. I settled on RL7 and am shooting 11.5 grains under a 210 Amax

 

[matthias]

Marine pmi - the time of bullet in bore is very similar to my 22 lr target gun. It shoots sub sonic eley and has a similar barrel length. So follow through is very important like you said. I have been trying different holds on the gun and there are two that really shine vs the others. The first is prone hard hold , then firm relaxed on the bench. Really touchy like you said.

Bugholes - really working on loading for this thing. I have some Lapua brass I am going to convert then neck turn and anneal . Then I am onto every stupid trick I can find to get rid of the vertical. So far the 1680 has been most consist and for me. I just got a whole stack of 190 &200 Sierra match kings with the chrono and a good range day I am going to see if I can narrow down the most velocity consist and loads.

 

[pinsandpitons]

I don't have a solid image of what you mean by 'firm relaxed' from the bench. I think I know what you mean by hard hold prone, but could always use other perspectives. Anyway, I don't want to turn this thread into a discussion of marksmanship, but could one of you elaborate a bit for my benefit?

 

[matthias]

Yeah it's kind of like jumbo shrimp.

I basically set up the rifle on the bipod and bags and move close enough to the rifle that I am pre loading let bipod off the bench. So my shoulder is firm on the butt but I am relaxed. Easiest way i can think of to ensure consistant shoulder pressure without free recoil. Might just be regular bench shooting. Although most people I see shoot are adding rearward pressure via the shooting hand or butt hook. I am only leaning into the gun , resting my face , and pulling the trigger . Make sense? Really hard to discribe

 

[pinsandpitons]

Perfect. Ya, I totally get it. That's what I do off the bench most of the time. So been out for more groups yet? I shot about 20 subs the other day (at random range steel mostly) but the one 100 yd 5-shot group was ~1" with one flyer way low (like 3").

 

[MarinePMI]

Mathias,

Another thing I failed to mention, that you may wish to play around with is crimping the round. A Lee Factory Crimp Die (custom) can be had, or made from a .221 FCD. Neck pull can have quite a bit of effect. If you can't get a FCD for the 300BLK, you may try (and don't laugh) gluing the bullets in place with primer sealant. This used to be an old factory "trick" for more uniform neck pull for machine gun ammo (and meeting stringent MilSpec requirements for belt fed weapons that were extremely sensitive to variances). Again, just some ramblings...

 

[pinsandpitons]

That was my experience for sure. As I mentioned earlier in the thread, the crimp was the key to smaller groups in my .308.

 

[reeljob]

I have been extremely aggravated with the performance of sub loads in my ACC-SD 300 blackout. It has been very inconsistant. I have used diffirent powder and combos of bullets. Yesterday I shot a 100 yard group with factory Corbon subs with 220 SMKs and shot a 2" group. Today I changed the hogue stock with my HS that was on my 5R and tried again with the same factory Corbon and group shot a solid 3/4" @ 100. I have had expierence with subs in .308 and in the T.R.O.S. 300 Whisper and results have been good with both platforms. It is my finding that errors in shooters form, handloading regiment, and poor equipment will magnify with subsonic loads. I am satisfied with todays testing and feel more confident knowing the rifle will shoot I just need to locate another take off HS Precision or BC Medalist stock.
I had taken the time to reinforce the hogue and felt this to be a worthwhile effort until todays range trip. My previous thought was with the low recoil of this caliber the action would not be affected as drastically as with the .308 but my findings show the opposite. Bedding is critical no matter the caliber, goes to prove anything has to be built on a solid foundation!!

 

[pinsandpitons]

1" @ 100 is a good load for subs. You will drive yourself crazy chasing bugholes at that range. N110 seems to be my best powder that I run with 220 SMKs in the 1000 fps range. I did shot a sub moa group @ 100 a few days ago with 180 Hornady RN at 987 fps but the stars must have been lined up that day since it happend only once. From my expierence sub loading is a diffrent beast and consistancy in your process is critical. Sounds like you are on the right road though.

Was this with the AAC-SD?

 

[reeljob]

Was this with the AAC-SD?

Yes, with the ACC-SD