Not getting bolt lockback when suppressed

16 inch mid, it's ran totally flawless until throwing my can on. With an H2, I have tried a regular BCG, LMT enhanced BCG, every buffer spring imaginable up to and including a sprinco red, but 99% of the time the bolt won't lock back on an empty mag. It will lock every time without the can on, doesn't seem to be insanely overgased or anything. Not trying to throw anyone under the bus but it's a LMT MRP, and I think it could have been ported a little smaller.. but I am not getting a bunch of gas to face with the enhanced bcg, and it doesn't feel like it's beating itself up or anything.

I threw the upper on another lower (H2, carbine spring), and loaded up an assortment of different mags with 1 round and they all locked back. I know undergassed barrels obviously won't lock back, just at a loss here. I get that the bolt could be outrunning something...but I don't get why it won't work on a MARS lower, but will function fine on another.

I’m guessing you have tried this with different mags? Try different brands?
How about your action spring? Sounds like your bolt is outrunning you mag spring.

I have a BCM 14.5 middy suppressed that hates to lock back for some reason. It's not excessively overgassed with the can, and definitely runs on the leaner side without the can.

Could be a thing with the middy length. I know I've had carbine gas systems that were way more gassy feeling that didn't do the same thing.

It's likely your upper is over gassed with the suppressor installed, but lets take a look at the most telling fact-

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Originally Posted by Torquetard

...I threw the upper on another lower (H2, carbine spring), and loaded up an assortment of different mags with 1 round and they all locked back...I get that the bolt could be outrunning something...but I don't get why it won't work on a MARS lower, but will function fine on another.

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The problem is the mag catch. The mag catch isn't adjusted right. I've had the same problem with a couple of my lowers. If the mag catch doesn't hold the mag tight enough, the follower won't engage the BHO firmly. Without the suppressor, it works fine. But the added speed the carrier from shooting suppressed is knocking the follower away from the BHO. If you tighten up the mag release button a bit (probably from a half turn to a turn and a half) it will solve the issue.

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Originally Posted by MistWolf

It's likely your upper is over gassed with the suppressor installed, but lets take a look at the most telling fact-

The problem is the mag catch. The mag catch isn't adjusted right. I've had the same problem with a couple of my lowers. If the mag catch doesn't hold the mag tight enough, the follower won't engage the BHO firmly. Without the suppressor, it works fine. But the added speed the carrier from shooting suppressed is knocking the follower away from the BHO. If you tighten up the mag release button a bit (probably from a half turn to a turn and a half) it will solve the issue.

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I actually did try that, but only gave it one turn. I gave it another one and it's just about as tight as it will go now. I'll see if it helps next time, thanks

Another thing I had an issue with was the bolt catch spring. I had one lower years back that I had to trim the spring because, compared to other known lowers, it was way stiffer.

Interesting. Don’t think I have seen that issue before. Good to know though.

Quote:

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Originally Posted by MistWolf

It's likely your upper is over gassed with the suppressor installed, but lets take a look at the most telling fact-

The problem is the mag catch. The mag catch isn't adjusted right. I've had the same problem with a couple of my lowers. If the mag catch doesn't hold the mag tight enough, the follower won't engage the BHO firmly. Without the suppressor, it works fine. But the added speed the carrier from shooting suppressed is knocking the follower away from the BHO. If you tighten up the mag release button a bit (probably from a half turn to a turn and a half) it will solve the issue.

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Double....

I'm having an issue with a mars lower MRP upper not locking back, it was sent in and they could not duplicate the problem so nothing was done. Noveske barreled upper and it locks back consistently. Both 16" mid length, neither suppressed. They can be finicky I'm thinking.

Think I found the problem. Is this out of spec, because on the other lowers I've tried the catch covers more of the bolt face. Can't get an answer from mfg, so if a BRT gas tube doesn't fix things (its actually retardedly over gassed anyway) I'm just going to hope they fix it.
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