Coworker got a ruger mpr that ran fine the first time to the range
On the 2nd time the bolt was not going back far enough to strip the next round, so it would dent the round and get jammed.
The gas key was ok, the fsb was ok....no leaks
The RO helped him trouble shoot. Tried different ammo, different mags, my spare lower, my spare upper and my spare bcg. They came to the conclusion that the bcg was the issue (and stacking tolerances). His bcg would work in my gun but not in his. My bcm bcg worked in both of our guns. The ruger uses a different bcg (unshrouded). I’m guessing the unshrouded bcg has more drag than a shrouded bcg as goes back over the hammer
My coworker noticed that my gun (bcm upper, Anderson lower with psa lpk) seemed easier to run the charging handle compared to his gun. The latter part of the pull was slightly harder. (I think no mag was installed and the hammer was cocked). I’m thinking the buffer spring is slightly stiffer than an in spec spring
I’m thinking the gun has tolerance stacking issues. When new it ran ok....maybe just barely. I’m thinking the chamber is a little out of spec and and wasn’t cleaned enough so extraction was harder the 2nd time it was used.
My coworker did mention the gas rings were pretty filthy. Ar’s are generally filthy so I don’t think that was an issue
I’m guessing the issues with the gun are an out of spec chamber, out of spec buffer spring and the different bcg cause the bolt slow down enough to cause the failure to feed.
I’m also guessing the rifle gas on an 18” barrel (lower pressure) combined with a carbine tube, carbine spring and carbine buffer (stiffer than a rifle tube set up right?) don’t help
My co worker already got a bcm bcg and will be testing his gun this weekend.
I’m thinking if he got a lighter buffer spring (tubbs?) or a lighter buffer (kac $$$)
Edited to add:
My upper is a 14.5” mid length with a carbine buffer if that matters
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