Subsonic accuracy problems

Moderators: gds, bakerjw, renegade, bamachem

Nathan-UK
Silent Operator
Posts: 83
Joined: Sun Dec 30, 2012 8:15 pm

Subsonic accuracy problems

Post by Nathan-UK »

Hope someone can spot the error here.

I am loading 8.5grn of Lil'gun, Hornady brass, CCI small rifle and 220grn Sierra Matchking HPBT. I have taken the COL from the Hornady website of 2.260". No crimp has been put on the cases and the bullets are secure.

The problem is that at best I am getting a 4" group at 50m with some of the bullets not going in square showing some signs of tumbling. They are being shot out of a 12" 1:8 twist barrel through an Ase Utra CQB suppressor. Removing the suppressor makes no difference.

I am inclined to think that the COL is too great as others on this forum seem to go down as low 2.1"

Any ideas and if it is the COL, what should I use?

Nathan
tallburnedmidget
Silent But Deadly
Posts: 3808
Joined: Wed Jun 13, 2012 9:01 pm

Re: Subsonic accuracy problems

Post by tallburnedmidget »

Changing your COAL would be a something you could investigate but you may want to work back incrementally watching for pressure signs to avoid any dangerous situations.

Also, do some searching on the forum about the benefits of using annealed brass and crimping 300 Blk rounds. From what I recall reading the two have significant impact on the consistency of a load (extreme spread [ES], standard deviation [SD], avg speed, etc.) and seem to be a best practice for the 300 Blk.

Wish I had more for you but hopefully this information will bear some fruit :)
User avatar
darr3239
Silent But Deadly
Posts: 338
Joined: Wed Apr 06, 2011 1:53 am
Location: Arizona

Re: Subsonic accuracy problems

Post by darr3239 »

Most are using Lil Gun powder for super sonic loads. Here is AAC's suggested subsonic load. They are the ones who developed the cartridge.

• R-P 300 AAC BLACKOUT brass
• Remington 7.5 primers
• 11.2 grains of A1680 powder (Adjust powder charge down as needed. Factory ammo is 1010 fps for 16" barrel)
• Case length is 1.368 +0.000 -0.020
• Sierra 220 MK loaded to 2.120 OAL (this length is optimal for reliable feeding from USGI magazines)
• Chamber pressure 21,100 psi.
"We, the people are the rightful masters of both Congress and the courts, not to overthrow the Constitution, but to overthrow men who pervert the Constitution." Abraham Lincoln
Retooferab
Senior Silent Operator
Posts: 125
Joined: Wed Mar 10, 2010 12:23 pm
Location: Arkansas

Re: Subsonic accuracy problems

Post by Retooferab »

I'm using 2.09 oal but I'm using N110 powder. 8.6 grains
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well armed lamb contesting the vote." Ben Franklin
User avatar
M_Derelict
Silent Operator
Posts: 67
Joined: Wed May 02, 2012 5:39 pm

Re: Subsonic accuracy problems

Post by M_Derelict »

Hey OP, which CCI small rifle primer are you referring to?
CCI400?
CCI450?
CCIBR4?
CCIM41?
User avatar
yondering
Silent But Deadly
Posts: 711
Joined: Thu Aug 02, 2007 12:22 pm
Location: NW Wa. state

Re: Subsonic accuracy problems

Post by yondering »

Nathan-UK wrote:Hope someone can spot the error here.

I am loading 8.5grn of Lil'gun, Hornady brass, CCI small rifle and 220grn Sierra Matchking HPBT. I have taken the COL from the Hornady website of 2.260". No crimp has been put on the cases and the bullets are secure.

The problem is that at best I am getting a 4" group at 50m with some of the bullets not going in square showing some signs of tumbling. They are being shot out of a 12" 1:8 twist barrel through an Ase Utra CQB suppressor. Removing the suppressor makes no difference.

I am inclined to think that the COL is too great as others on this forum seem to go down as low 2.1"

Any ideas and if it is the COL, what should I use?

Nathan
I'm not sure anyone here actually read your post.

If you're seeing some bullets tumbling, the problem has nothing to do with COL, powder or primer choice, etc. Your barrel is not stabilizing those bullets, at that velocity (or you're getting contact between the bullet and a baffle or brake, don't know how you're can is mounted?). Try a shorter bullet, or a different barrel.

I know, a 1:8 should stabilize that load, but some barrels stabilize better than others, just the way it is.
Nathan-UK
Silent Operator
Posts: 83
Joined: Sun Dec 30, 2012 8:15 pm

Re: Subsonic accuracy problems

Post by Nathan-UK »

The suppressor is a borelock one. The barrel is fitted with a flash hider that has threading behind it so the suppressor screws over hte flash hider. There is a colar then that locks it in place. My first though was that I may be clipping the baffles but I get the same problem without it. I was rather hoping that a deeper seating or maybe a slight crimp would allow the pressure to build up more evenly so that the bullet accelerates more quickly. One thing that I haven't tried yet is to chrono the rounds which is the next step to make sure that they are doing around the 1000fps mark.

If if turns out that the barrel simply doesn't like the bullets, I will drop down to 200grn and try that. Does anyone have a load and COL for a 200grn Sierra MK with Lil'gun ? Hodgdon don't show a load on their site for 200grn. Or should I move over to A1680 powder?

Thanks for the help so far.

Nathan
User avatar
farm use
Silent But Deadly
Posts: 1271
Joined: Tue Oct 09, 2012 2:48 am
Location: SW virginia

Re: Subsonic accuracy problems

Post by farm use »

Yonder is right, its not stable. I would try A1680. If that doesnt help then I would try a lighter bullet. I love the 208gn amax. I would NOT use the suppressor until you have them stable.
bani
Silent But Deadly
Posts: 475
Joined: Tue Feb 28, 2012 3:33 am

Re: Subsonic accuracy problems

Post by bani »

Nathan-UK wrote:Hope someone can spot the error here.

I am loading 8.5grn of Lil'gun
there's your error.

use 1680. done.
45r
Silent But Deadly
Posts: 390
Joined: Sun Sep 25, 2011 8:30 pm

Re: Subsonic accuracy problems

Post by 45r »

You should be able to get better groups than 4 inchs.1680 is the best powder for subs.If you want best accuracy it's good to anneal your brass and turn the necks.Brass reformed from 223 often have lop-sided neck thickness.
Annealing and neck-turning is time consuming but not hard once you get a little experience.It often shrinks groups when using reformed brass.
You might have something else going on with your rifle.Some of the very good groups some show are often people who use bench rest type reloading skills.
Post Reply

Who is online

Users browsing this forum: Bing [Bot] and 114 guests