On the last round of every mag, the bolt is not catching. I'm not using a BAD lever or anything. This occurs 100% of the time.
The lower that I'm using is a Mega forged lower with Grant's LPK (LMT parts, right?) and a BCM carbine RE/spring with an H2 buffer. The upper that it's being used with has been tested with two other lowers without having any issues. Upper is a 16" mid-length, made from BCM/DD parts, and the gas system was checked out by ADCO. So far I've sifted through a few things that could cause problems:
1. It's not the mags, I went through 8 different mags/types.
2. System isn't over/undergassed, ejection is fine (ejects 3 o'clock).
3. Isn't ammunition (XM193)
4. Isn't the BCG, gas key and rings are fine.
The upper ran fine with another lower on a Vltor A5 system. So I've narrowed it down to this:
1. Buffer is too heavy (H/H2 were tried, haven't tried a standard)
2. Bolt catch, spring, or plunger is defective (Bolt catch will hold/release fine when pressed/depressed)
3. Out of spec lower
Are there any other possibilities for problems? I'm not sure if it's a buffer weight issue because I've ran this upper with an A5, which is heavier. One thing I'm noticing is that the bolt catch sticks out halfway when it fails to catch the bolt.
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