Impossible 300 Blackout accuracy issues

[300blak]

Hello all. I've been lurking on here since I started casting several years ago and have learned a ton. But the one round I cannot get to shoot accurately is a heavy 300 blackout subsonic load. I've tried the controversial lee 230gr and have recently tried a NOE 311-242-FN. After trying both in just about every load variable I know, I can't get below 3.25 MOA @ 100 yards. Is this as good as it gets with these missiles? Definitely not looking for sub-moa, but 2 MOA would be nice. I've searched this forum as well as 300blktalk and havent found a definitve answer. I need help from the Boolit masters. Been chasing this issue for over a year on and off.
For starters I'm using :
8.5" 300 blackout radical firearms upper 1:7 twist
YHM resonator suppressor
either a 100% COWW or 50/50 COWW/SOWW boolit (accuracy hasnt changed appreciably)
Accurate 1680 powder anywhere from 10.8-12.2 grains
Powder coating the boolit nose down as well as nose up
Seating depth from 2.180-2.250
Sized to .310 with a reamed lee sizer (slugged bore is ~.3075-.308)
No gas checks
Light crimp to remove case flare from Lyman M-Die

What did I miss?

[cas]

I will be of no help. But I've been shooting the 300/221 for well over 20 years, mostly super sonic, jacketed bullets. I've owned 4 single shot pistols (and worked with 2 others), 1 single shot rifle, 1 bolt action rifle and 4 AR's in it in every name it's been called. Out of all of them, only two have been just barely MOA shooters and it took lots of load work to get that. Maybe there are real accurate ones out there, but they've never crossed my path.

Adding cast and sub sonic into the mix, it doesn't surprise me.

[Forrest r]

That lee bullet design is +/- 90 years old. Didn't work then & it still doesn't work to this day.

[Goofy]

You bit off a chunk with the project.

7” twist w/cast? Good luck.
8.5” barrel chasing MOA @ 100? Good luck.
Bore is .3075-.308”? What’s the groove diameter?

[Wisest.fool]

I am also interested in the answer to this question. I have achieved about the same with a cmmg upper and the lee 230gn sized .309. It is acceptable for my purpose, but i wouldnt mind tightening them up.

[John McCorkle]

Have you had success with the gun in either super or subsonic in any jacketed or other cast load?

Trying to determine if you are finding issues with loads or with the barrel itself...also, when you chamber a round, have you tried to pull it from the chamber and look at the nose of the previously chambered round?

Those looong boolits in a short case act like a fulcrum and lever and put alot of pressure on both the nose or/and on the neck which can push it slightly out of concentricity....at least it has for me in testing a time or two.

Alot can depend on your feed ramp geometry and in my case seating depth chang just a little made the difference.

Sent from my moto g(7) power using Tapatalk

[Burnt Fingers]

I have a 7" 300 BO upper that plain would not shoot cast at all. Went to a 10" and the results are MUCH better. Even better when the boolit is gas checked.

[Ford SD]

Still working on loads for my 2 bo /bolt and semi

I will note that neck thickness of the brass can be a factor (sizing down lead rounds)

Neck thickness of 10/11 thou is good and what I use for my cast loads

if I convert any brass and it has the 12-13-14 thickness I use it only for jacketed rounds

I have also been water dropping for these loads

with the molds I have I have had full function in the semi with weights over 165g

[300blak]

You know it’s been so long since I shot some real jacketed I honestly can’t remember. I’ve never shot super through it since I’ve owned it. I’ve thought that might be the answer to see what the gun can be capable of

[300blak]

[QUOTE=Ford SD;5090664]Still working on loads for my 2 bo /bolt and semi

I will note that neck thickness of the brass can be a factor (sizing down lead rounds)

Neck thickness of 10/11 thou is good and what I use for my cast loads

if I convert any brass and it has the 12-13-14 thickness I use it only for jacketed rounds

-I just checked my neck thickness from my converted 5.56 Lake City brass, Aguila and Winchester and the LC is 11.5 thousandths, aguila is 11, Winchester is 11.5,

[Ford SD]

For brass conversion, before you have problems cut down 1-2 and check neck thickness

= test a few

I have some 556 brass and when you cut it down it is 14-15 neck thickness,...... so 223 only

not worth my time to do neck thickness trimming

I have the dillon swager and it does the best job ( i think) on those crimped primer pockets

[jimb16]

Just remember: as a general rule, the longer the bullet, the faster the rate of spin needed to stabilize it. That is why it is such a pain trying to get tight subsonic groups with those long heavy bullets. I wish I knew the answer. I wonder if anyone makes a long heavy bullet with fins??? (Only half kidding)

[dverna]

A pistol that groups 4 MOA with cast bullets is not that bad IMO.

In spite of reports to the contrary...not many bolt action rifles will hold 2 MOA with cast bullets.

I would at least try Jacketed bullets in the gun before getting too worked up. It could be a gun issue but I doubt it.

[PositiveCaster]

What did I miss?

Powder. Your AR may not like AA1680. My .300 likes it but yours may perform better with another. Have you tried H100 or Lil’Gun? Are the holes in the target perfectly round? That bullet may need more velocity with that twist, what is your current velocity? I found with 220-grain bullets in my .300 I needed a higher velocity to get better groups.

Then again, maybe 3-4 moa is all your barrel is good for shooting any cast load. Another thing you’ve missed. Hopefully you can get down to ~2 moa.




.

[Mk42gunner]

Don't have one, don't really want one; which means if someone gave one I would take it and shoot the heck out of it.

7" twist, I would try adding a gas check first. It may help, I highly doubt that it will get to 2MOA, but its worth a try.

Robert

[300blak]

Don't have one, don't really want one; which means if someone gave one I would take it and shoot the heck out of it.

7" twist, I would try adding a gas check first. It may help, I highly doubt that it will get to 2MOA, but its worth a try.

Robert

I’m a little Leary of using GC’s with a can. Don’t really want it dinging a baffle.

[Nobade]

Try VV N110. We have seen the best results with that, far better than 1680.

[RU shooter]

Imo that's not bad accuracy for that gun and cast bullets at 100 yds . Before I got all twisted up saying why won't it do better I would shoot a few groups with heavy jacketed bullets at the same range as a bench mark .

[yovinny]

Ive heard lots of stories,, but have yet to personally see anyone do better then about 2.5moa with anything subsonic in a blackout...
Supersonic on the other hand, can pretty easily cut that in half.

[Larry Gibson]

Use Hornady crimp on GCs. They will stay on with subsonic loads.

[popper]

Didn't say what sights you used. 1:7 is OK but 1680 doesn't burn right/complete in the barrel. Plus it' a AR pistol! 2400 should work better. The Lee doesn't get any rave reviews. Might stay with COWW. PC & WD@309. IMHO you're doing fine 3"@100. Might try single loaded not from mag to see if nose gets 'bent'.

[Burnt Fingers]

Didn't say what sights you used. 1:7 is OK but 1680 doesn't burn right/complete in the barrel. Plus it' a AR pistol! 2400 should work better. The Lee doesn't get any rave reviews. Might stay with COWW. PC & WD@309. IMHO you're doing fine 3"@100. Might try single loaded not from mag to see if nose gets 'bent'.

So if I'm loading 9mm for a 9mm RIFLE I should use rifle powders??

[Wisest.fool]

I am no OP but now that i have seen all these suggestions i am gonna try a few in my 16" cmmg upper.

Gas checks i havent tried.

Seating depth i havent tried. I just made sure they would fit in the magazines.

And im using imr 4227 and lil gun if i get better results i will post it here.

[sigep1764]

So if I'm loading 9mm for a 9mm RIFLE I should use rifle powders??

Burnt, I believe Popper was referring to 1680 not being able to generate a complete burn of the powder load because the barrel is short. I also believe he was referring to the Pistol Length gas system needing a lot of gas fast and that 2400 could achieve this. I do not think it was a matter of the specific cartridge in a rifle or pistol.

[sutherpride59]

Boy howdy when you find the secret to really accurate subsonic 300 AAC loads let me know lol. I’ve only don’t a tad better than you with my 16” barrel. Gas checking eliminates the lead fouling in my suppressor but doesn’t do anything for accuracy IN MY GUN so I always use them. As others stated seating depth is a thing. I have had issues with large velocity spreads in mine using H110 or 300CFE. I ladder tested some with W231 just to see how quiet they would be and when I have some time I’ll test them for accuracy too. Just need to have that “free-time” I keep hearing about lol.

[popper]

2400 will give good burn in 7". Tried cfe p, 1680, 2400 in my pistol, 2400 worked best and would cycle, 170gr PB. I assume a scope was used for 100, but real problem is a pistol is really hard to shoot 100 for testing as a stable shooting platform is hard to make. I've read about 44mag pistols hitting hogs in the shoulder @ 80 yrds free hand - maybe but not me. 3x scope@ 50 with bipod - 2400 does cycle, this is ~1k fps. I would need a 9x scope for 100. Add an extra ~7" drop @ 100 for this load, energy is only 330 ft-# terminal and 440 ft-# for 240gr. Not even legal for deer hunting in some states. IMHO the OP goal is on the ragged edge.
275714

[300blak]

That’s correct on using a scope. Vortex Strike Eagle 3-9x40. I’m shooting it prone with a rest to eliminate as much error as possible. If I can scrounge some 110 or 2400 I’ll give it a shot as well. Trust me. If anything works, I’ll post it here. I use Gordon’s Reloading Tool and that is a correct statement that the 1680 is not a consistent burn. From my specific data, it’s only showing a 74% burn rate.

[Lloyd Smale]

like larry said use a hornady or gator check they stay on and get the soft lead is better idea out of your head. If all you have is ww then water drop it. With pc its easy. Just take your bullets out of the oven and dump them in cold water. A 1-7 twist is to fast for soft bullets. they are probably stripping through the rifling. I agree with yovinny to a point too. Sub sonic loads arent meant to shoot at a 100 yards. There mostly up close and personal sneak in shoot and sneak out rounds. That said i do have a sub sonic load that shoots but its no good in an AR. My ruger american with a can on it shoots the 130 rcbs spitzer gas check bullet with 4 grains of unique into under 2 inches at a 100 yards. Trajectory is like a rainbow though but its pretty cool as its no louder then a pellet rifle. Much less noise then the bolt slamming back and the springs compressing and slaming it back in an ar and quieter even then the sub sonic 200 plus loads with powders like cfe blk and 1680.

[popper]

300blk - thinking maybe powder burn in the can may lead to loss. Post targets pic we might be able to determine what is going on, horiz/vert stringing, shotgun, etc. I use GRT too. I use a bipod for testing but your short barrel doesn't have much to hang on to, I get a little jump from my 10", mostly bolt movement and torque reaction from spin.
power pistol or accurate #7 might work also. H110 I don't download!