Sub sonic accuracy

[matthias]

I have been working very hard with 300 blackout 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

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

 

[bricktop]

What for powder are you using for subsonics?

 

[matthias]

Lil gun , h110 , 1680

 

[284driver]

Vv n110 seems very consistent with the heavies for me.

 

[madderg]

sub-sonic rounds have a slower more pronounced oscillation of the barrel...throwing wider patterns for group. Something to try that cost no money!! slip a 2X2 inch piece of closed cell foam sheet, like the stuff they wrap shipped items in, under the barrel at the end of the stock. It will take a lot of the oscillation [vibration] out of the barrel and the groups should shrink. Give it a try and get back to the post on your results.

 

[eww1350]

The AAC blackout is using a 1 in 7 twist...there is a barrel for sale on Ebay that is a new take-off...might be better for subsonic with a faster twist...

 

[germanlongbow]

I shoot a 300 blackout with ar stoner barrel 16 inch. Subsonic loads over 1680 powder and 220gr sierra matchking work very well. Consistent 3/4moa 5 shot 100 yard.

6.5x284 with 1680 and 140gr SMK produce 3 shot sub 1/2 moa as well with 26 in barrel. Also good luck with Trailboss. Work great in bolt rifles but not auto's. Scary quiet with suppressor on. Hope this helps. Scott