300 AAC Suppressed SBR reliability question

[armedpolak]

I have an integrally suppressed AR upper in 300 AAC: https://www.radicalfirearms.com/product-p/rfisu300.htm it doesn't have a gas block that can be regulated, the barrel length is 8.5" internally and uses pistol gas port position. I measured the gas port and if I remember correctly it measured 0.110 inches.
I'm using low-mass BCG for it: https://www.midwayusa.com/product/1025208743?pid=979730
And I recently purchased JP Silent Captured spring with 3 metal weights and standard spring, though I have 2 tungsten weights and spring kit arriving soon.

The issue is that ever since I installed a new 2 stage trigger and a bolt stop extension (this one: https://magpul.com/bad-lever-battery-as ... _color=118) the rifle has been utterly unreliable with 200gr to 220gr subsonic ammunition: it would not lock back after the last shot and often times it appeared to partially strip the next round then jam it half way with the bolt, or not chamber the next round at all.

So far I tried to remove buffer weights (before I got the JP spring) and it helped a lot but issues still persisted. Few days ago I tried it again with the JP spring in default configuration and it was acting up every 2nd or 3rd shot, then JP spring with no weights and it was still jamming. I thought I was onto something with the reduced buffer weight but it appears the bolt may be moving too fast or something.

My question is how to properly tune such setup? I read different opinions online, some to decrease weights and use lighter springs, some to increase weights but use lighter springs, and some to increase both weight and spring strength. I'll have the spring kit and additional weights soon and want to hear your opinion on what to try first. Should I start with H2 weight and a lighter spring for example and go from there? I also don't recall the ejection patters but remember lots of gas blowback and very dirty brass indicating the system is over-gassed, likely due to me reducing the weights.

I don't much care for supersonic ammo in this gun but want it to be 100% reliable with subsonic.
I also read on JP's website that the Magpul bolt catch extension may be causing issues because it slows down the speed at which bolt stop moves up to catch the bolt, and JP recommends a lighter spring if using said attachment.

Please help

[Arkhangel5]

AP,

Just from my experiences(limited) with ar's and suppressed, sounds like you are overgassed. I would try going heavier on the buffer and spring, since you cannot adjust from a gas block. I used this to slow down a 6.5 creedmoor that displayed same issues as you described, using a combination of heavier buffer, heavier spring and then adj block to get it running 100%.

That said, you mentioned you changed 2 items, i would start there, remove 1 and retest and see if issue goes away first, then the other. Eliminate them as the issue first.

My 2c,
SY

[armedpolak]

AP,

Just from my experiences(limited) with ar's and suppressed, sounds like you are overgassed. I would try going heavier on the buffer and spring, since you cannot adjust from a gas block. I used this to slow down a 6.5 creedmoor that displayed same issues as you described, using a combination of heavier buffer, heavier spring and then adj block to get it running 100%.

That said, you mentioned you changed 2 items, i would start there, remove 1 and retest and see if issue goes away first, then the other. Eliminate them as the issue first.

My 2c,
SY

thank you, and yes I agree the system appears to be over-gassed and I've been going about it the wrong way by decreasing weights. I'll receive the additional weights and springs for my JP spring system and will start by installing 2 tungsten weights that will give me the equivalent of H2 and a heavier spring. I'll take all the parts with me to the range and will give it a try until I figure it out. I don't really want to swap out the trigger just yet, it's a very nice high end 2 stage trigger and rather run the rifle with it, but will bring tools need to remove the bolt stop extension and test with and without it.

I'll post my results here. btw the manufacturer told me they never tested with low mass BCG and in fact supplied the upper with standard weight BCG and recommend H1 buffer weight; I was always running it with lighter mass so I'll start with H2 and see what happens; but I'll bring the original BCG with me since I found it in my spare parts box and see if using it is the only way to fix the issue. then again it was acting up with it in the past so perhaps I can stick with low mass one.