SBR extraction issues?

yournamehere · Mar 15, 2016

300blk
9" barrel
Vltor A5 with h2 buffer
Regular gas block
Pistol length gas

Unsupressed it does not eject the fired round, bolt goes back far enough to pick up the next round and jams. Same results with 150gr fiocchi and 220gr Remington.

Suppressed it runs perfectly with either ammo.

Suggestions?

AACo · Mar 15, 2016

I'm sure someone with more knowledge will chime in shortly.

Without suppressor, fire one round with an empty mag. Does the bolt lock back? If so, gas shouldn't be an issue. If it doesn't lock, try a lighter buffer.

clandestine · Mar 15, 2016

Put in a standard weight buffer without the can and see if it will cycle.

Its undergassed from your description.

yournamehere · Mar 15, 2016

clandestine said:
Put in a standard weight buffer without the can and see if it will cycle.

Its undergassed from your description.

Can I use a carbine buffer in the A5 tube? Or should I pick up the A5 H1 buffer(4.56 oz)?, the h2 is 5.3 oz.

Thanks for your advice, it is appreciated.

SCARCQB · Mar 15, 2016

Run the lightest buffer and spring with unsuppressed shooting. Low mass bolt carriers also help.

The 300blk with 9" barrels aren't designed to run unsuppressed. Its is optimized to run with a can and subsonic loads.

clandestine · Mar 15, 2016

I assumed you were using a H2 Carbine Buffer in your A5 (Not the longer A5 Buffer). This can be done with a spacer when using an A5 tube.

If you are using a H2/A5 Buffer, then its almost certainly the issue. I dont think the H1/A5 Buffer will alleviate your issues, you need a lighter buffer.

If it were me I would install a Tubb Action Spring first and test with the buffer you have. If that does not work I would use a standard carbine buffer (3 steel weights) and use a spacer in the back of the buffer tube (quarters) to limit bolt travel. If you dont use a spacer the gas key will hit the lower when the gun cycles which will break gas key screws.

SCARCQB · Mar 15, 2016

A quick fix is to run a lightweight buffer and a krinkov style brake.

The krinkov brake is designed to function as a secondary blast chamber to enhance the back pressure and help with undergassed systems mostly encountered with short barrels

yournamehere · Mar 15, 2016

Thank you gentlemen, lots of good info here.

I already have a Tubbs flat wire sitting here for another build, so I will try that first.

Can is a YHM ti phantom. I have the YHM qd flash hider installed. Would I see improvement with changing to the YHM qd brake?

clandestine · Mar 16, 2016

The YHM brake will not generate much, if any back pressure. Stay with the YHM Flash Hider.

SCAR is right, a Krink Brake (Booster) will make the gun cycle, but there is none that fit over a YHM at this time to my knowledge.

yournamehere · Mar 26, 2016

Replaced the buffer spring with the Tubbs flat wire and still the same issue. Ran short on time at the range and did not try changing to a standard carbine buffer with quarters. I'll give that a go on the next range trip. I did switch out uppers to a 10.5 556 and it ran fine suppressed and unsupressed.

Thanks for the pointers

SBR extraction issues?

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