Help with Suppressed SBR Malfunctions...

[JSGlock34]

I recently purchased a AAC M4-2000 suppressor to pair with my SBR, a Noveske MK18 upper mated to a LMT lower. I've owned this SBR for many years, used it in carbine classes, and it has proven very reliable (unsuppressed). However, the addition of the suppressor has introduced numerous bolt over base malfunctions when shooting suppressed. I haven't been able to make it past 2-3 magazines without a bolt over base malfunction.

I've steadily increased the buffer weight, going from H to H2 and finally H3 (all Colt buffers). I also replaced the recoil spring with a fresh Colt spring, and when the problems continued I tried Sprinco, first the blue spring and finally the red. The combination of the H3 buffer and the red spring looked promising, but didn't last 100 rounds before the bolt over base reared its ugly head again.

I'm using GEN2 and GEN3 PMAGs and have no magazine related issues to report. The problems occur with multiple magazines. The rifle is well lubed with FireClean. I am shooting Federal Lake City XM193.

Welcome any advice as to next steps.

[Jay Cunningham]

My 11.5" BCM cycles .223 Wolf completely reliably with an A5H4 VLTOR buffer... 6.83 freaking ounces.

You're tapping very high pressure gas and I don't think you can go too heavy with your spring/buffer combo. Possibly consider an LMT Enhanced Carrier.

[JodyH]

I use a steel Colt 9mm buffer with 3 tungsten weights and a Wolff + spring in my suppressed 10.5".

[JSGlock34]

Thanks - I was researching the LMT Enhanced Carrier earlier in the day. Trying to parse whether you should use it in barrels shorter than 14.5" was making my head hurt, but it seems like some users have reported that it has helped with suppressed SBRs.

[JodyH]

Bolt over base is usually a gassing (can be under or over) issue not an extraction/ejection issue. Enhanced bolt/carrier probably won't do much for you.

[Jay Cunningham]

The LMT Enhanced Carrier vents extra gas.

[JSGlock34]

Is the 9mm buffer enough over the H3 to make a difference? Looking at Midway, they're list H3 as 5.4oz and 9mm as 5.5oz...

[Default.mp3]

Slash makes some extra heavy buffers: http://heavybuffers.com/ar15carbine.html

You could also try switching out your receiver extension for a Vltor A5 setup.

[PT Doc]

I run one of Slash's H4 buffers with a Vltor A5 and a green Sprinco rifle spring on my 11.5 with a Surefire SOCOM mini. Very smooth and totally reliable through about 3k rounds.

[punkey71]

OP, have you considered an adjustable gas block?


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