.300BO carbine wont fully cycle with subsonic ammo, do I need a new bufffer spring.

[koger]

I have 2 AR's, in 300BO. One had the pistol type gas block and functions anything I have run thru it, even some very light subsonic loads. The other one will fire, eject the case, but does not come back far enough to pick up another round when shooting subsonics. It has the gas block out about 10 inches, the one that works with anything, about 7.5 inches, from the receiver. Do I need to change springs, and what do I need to get. All replies appreciated.

[popper]

Standard carbine BO? Called short stroking - does charge handle go back all the way easy - long spring? Is the lock back tab free? Add 1/2 gr powder to see if just too light a charge to work. What powder and bullet?

[koger]

I went from 8.3 grs of lil gun up to 9grains, and it still didn't function correctly. I am thinking it needs a lighter spring? The last 25% of the pull back on the bolt is a little stiff, but not too bad.

[Texas by God]

Remington factory subsonic loads won’t function my 16” carbine gas .300 BO always- but I like lightweight supersonic in it better anyway. I think I’ve read that pistol gas system is the way to go for subs, that’s the difference you have it seems.

[1Hawkeye]

Another trick you can try is to remove one of the weights from inside the buffer. This will allow the bolt carrier to generate a little more force on its rearward stroke.

[popper]

Check length of spring. May be too long. GS put together an ar10 and the spring was too long. Same symptoms, and hard to get C handle all the way back, scrunching the spring.
My BO carbine shoots the UMC subs fine.

[Loudenboomer]

How long is the barrel with carbine length gas system? Are you using a suppressor with these subsonic loads? Bullet weight? More info may be helpful but you could try a spring change, Adjust buffer weight, seat bullets slightly deeper if they will feed or try an adjustable gas block. The first thing I would try is AA1680.

[sukivel]

I would try a different powder first.


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[Gtek]

The experience with this round I have had is you must decide what round you intend to shoot and buy or build to it. The 300 is a great intermediate round but it lives in little boxes when pushed through a gas gun, a bolt/single poke gun you just load to speed/twist considerations. A gas gun (AR platform) there is a steep learning curve, sounds like you have pistol and a carbine gas. Pistol for your sub fun and carbine gas will work bottom end usually/sometimes/almost with a linear or a can but kind of on ragged edge with slow and heavy. If it is a 16" carb gas they are fantastic for 125-150 supers and an adjustable gas block is nice for both. Spring is about just a spring in extension, gas type/management of and buffer weight with a little barrel length thrown in are the biggies.

[Shiloh]

More powder, different powder, lighter spring.
The issue with lighter springs, is they need to be changed back for hotter ammo.
Best if you correct the issue by fixing the ammo.

Shiloh

[Winger Ed.]

I'd add a 1/2 grain of powder at a time until it cycles reliably.

Sounds like your charge isn't quite power full enough.

[popper]

The spring should only be strong enough to force the bolt closed from lock back. Gas pressure opens the bolt and forces it back, spring and buffer control speed of bolt. If too fast, next rnd doesn't get picked up right. If light gas, bolt doesn't go back far enough. What ammo?

[Finster101]

Try 1680.