I believe the reason for the fast twist rates in the .300 is because the round has been envisioned from it's inception as using suppressed, subsonic, heavy bullet...not the lighter weight bullets you’re using–particularly from the shorter barrels like you’re using.

I think some of the longer barrels have slower twists; I’ve got a 14.5” Ranier barrel in .300 which has (iirc) a 1:9 twist...shich reminds me...I’ve gotta either do something with that barrel, or get rid of it...

 

I believe the reason for the fast twist rates in the .300 is because the round has been envisioned from it's inception as using suppressed, subsonic, heavy bullet...not the lighter weight bullets you’re using—particularly from the shorter barrels like you’re using.

I think some of the longer barrels have slower twists; I’ve got a 14.5” Ranier barrel in .300 which has (iirc) a 1:9 twist...shich reminds me...I’ve gotta either do something with that barrel, or get rid of it...

Not sure what's going on. I used a Nosler 220 gr at 1100 fps and still got the warning with a SF of 3.7. With a Hornady 220 gr the SF was 4.3 which also had the warning.

I clicked Ballistic Explorer's "Twist Rate" button for the Hornady 220 at 1000 fps and it calculated a twist rate of 11.5:1.

I backed the velocity down to 1000 fps and the Hornady SF dropped to 4.1 and still had the warning. So, I don't know what's up with the fast twist rates. CMMG isn't open yet (I don't think), but i will call them and see what they say.

 

The 300 BO was never intended as a range rifle IIRC. CQB. Minute of man, pig, deer to 150. Not minute of dime. :image035:

As stated above - Niche group rifle shooting large slugs, suppressed, and subsonic.

You could get a barrel cut to properly stabilize the bullet, but then what are you really gaining? One would think that this issue has been visited and evidently was a non starter or it would have been a corrected option for purchase.

 

Maybe, but I doubt anyone would be satisfied with a 3-4 MOA gun. CQB was one goal, but not exclusive. A rifle bullet properly stabilized should shoot to 1-2 MOA.

One of the guys big in the shooting/hunting game (big in hunting, not big game) shot an integral suppressed .308 bolt gun and got pretty good accuracy with it. He was making behind the ear hits on pigs.

I agree it is not a precision load, but I can't see why it can't shoot 1 - 2 MOA, and several people on this board are seeing that kind of group. I had an 8 shot, 1.5" group at 100 yards with factory ammo last time out. So I know it will shoot better than some of the awful groups I've been seeing from my gun and others I've watched shoot.

Should be interesting to see what happens today with stepped loads.

 

I still need to tweak my seating depth a little, but Im not having problems with it. I shoot a 110gr nossler varmageddon through a 8.5" 1:7 twist barrel

 

Well, that's encouraging! What kind of groups do you get? Thanks!

 

Well, I just got back from the range and shot some factory Hornady Black 208 gr BTHP subsonic at 50 yards - five shots in a three inch group. :ticking: If I add the first cold bore shot it's 6 shots in 6 inches. That's a 6 MOA group or a 12 MOA if I count the cold bore shot.

This is the same gun that shot 3 hits overlapping at 50 yards with Hornady Black 110 gr VMAX just day before yesterday and roughly 1.5 MOA groups at 100 yards. I was very pleased with that performance. The difference today was, like they say, night and day.

Oh BTW, I loaded 5 rounds with H110 and Speer 125 gr TNT HP bullets per the Speer Handloading Manual. I seated the bullets to 2.060 PER the manual - they would not chamber! A buddy had his blackout AR and they would not chamber in his either. It appears, that even though they are listed in the Speer manual under the 300 AAC Blackout, the bullet is too fat to chamber - even when seated to a COAL of 2.060" :blink:

 

I shot some factory 125s through mine and it grouped about like birdshot at 100 yards. I dont have a .30cal suppressor though so Ive never tried shooting subs. Maybe I need to buy one...

Looking here it looks like people use the 125gr tnt in 300blk. Is it possible the bullets are out of spec?

 

Well, now that we know what my problem was, I would add this. I have gotten a lot more consistent results with 16" barrels than the shorter barrels. That contradicts my over-stable theory since the longer barrel generates higher muzzle velocities and hence faster rates of spin.

I'll load up a few rounds tomorrow to see where I am and then run a 10 step charge test based around that.

Another interesting aspect of all this is that Hodgdon lists 21.0 gr of Lil-gun powder for the 125 grain bullet. When I loaded 21.0 gr of Lil-gun into a 300 Blackout case, it filled it to within about an 1/4" from the mouth!

This is listed as a compressed load, but while it looks like a lot of compression, it's not as bad as it looks. The bullet, seated per Speer's Handloading manual at 2.060" only protrudes into the case about 0.231", so what looked scary to look at, really isn't that bad.

 

Frustrating to read this thread. I’ve been considering going to a suppressed BO pistol for a home defense weapon. This is the first I’ve heard of accuracy issues. Although ranges within the home environment are short, I’m not excited about the accuracy issues you folks are having. I will not be handloading, so factory ammo is what I’ll be using.

Going to review twist rates rates in the current brand offerings out there. This will be a factory gun, not a self build. Please update your progress gentlemen!

 

300 BO pistol twist rates:
Daniel Defense. 1:8
CMMG. 1:7
Springfield Armory Banshee. 1:7
Sig. 1:5
Rock River. 1:8
PSA. 1:8

 

Look, Sig may have figured it out.

 

I got it! Well, the chambering issue, not the accuracy issue - yet!

In an attempt to put a light crimp on the case, the factory RCBS seating and crimp die, compressed the shoulder of the cases slightly instead of crimping the cases. I couldn't see it until I zoomed in tight with the camera on my phone. Then I looked at it through some magnifiers and sure enough, there was a very subtle bulge on the shoulder - that's why it wouldn't chamber! Thank goodness it wasn't the bullet!

A Lee Factory Crimp die will be here Sunday - that will resolve that problem!

 

Well at least you’re not this guy.

 

...Well at least you’re not this guy.

No wonder he's having problems - Hodgdon's max for a 168 gr in 300 BO with Lil-gun powder is 15.3 gr - not 19.1 gr! :blink:

 

Yesterday's result resulted in one load of the 10 stepped charges, 20.4 gr of Lil-gun with a 125 gr bullet, giving an accuracy of 0.845" at 50 yards with and ES of 2, and a SD of 1! :thumbsup" Average velocity 2039 fps, from a CMMG 8" barrel with a Liberty Victory suppressor. The suppressor is 2" longer than the barrel :blink:

Unfortunately, that 0.845" group that looks pretty good, is actually a 1.6 MOA. Not bad, but not what I'd like. However, that was with a 5x scope; it would be reasonable to suspect that all the groups would have been tighter with a higher power scope.

Plus, all the rounds were a mixture of Sig and Hornady once shot brass, unsorted, and I did notice variations in primer pockets and bullet seating effort. This morning I'm loading the same loads into Lapua cases and will use a 20x (or so) scope. It will be really interesting to see what happens this afternoon - in the rain no doubt.

 

Yesterday's result resulted in one load of the 10 stepped charges, 20.4 gr of Lil-gun with a 125 gr bullet, gave an accuracy of 0.845" at 50 yards with and ES of 2, and a SD of 1! :thumbsup" Average velocity 2039 fps, from a CMMG 8" barrel with a Liberty Victory suppressor. The suppressor is 2" longer than the barrel :blink:

Unfortunately, that 0.845" group that looks pretty good, is actually a 1.6 MOA. Not bad, but not what I'd like. However, that was with a 5x scope; it would be reasonable to suspect that all the groups would have been tighter with a higher power scope.

Plus, all the rounds were a mixture of Sig and Hornady once shot brass, unsorted, and I did notice variations in primer pockets and bullet seating effort. This morning I'm loading the same loads into Lapua cases and will use a 20x (or so) scope. It will be really interesting to see what happens this afternoon - in the rain no doubt.

Good Luck!

 

I was thinking the very same thing.