jaredm1
Ultimate Member
- Upper is 20" A4 (Bushmaster 1:7 govt. profile barrel assembled by PK Firearms)
- Lower is built from Del-Ton stripped receiver and RRA LPK
- Started with rifle-length buffer tube/spring/weight, then switched to carbine/entry length Sully Stock (behavior is the same with either set-up, so I don't think that's the problem)
- Mix of ammunition: Federal, Centurion, Fiocci, PMC, Wolf, Brown Bear
- Magazines include P-mags (20 and 30 rnd), and USGI (20 and 30 rnd)
In general, I will be set up at the range and the rifle will function 100% for the first 100-150 rounds, then begin short-stroking.
I usually save the steel-cased ammo for last (Wolf, Brown Bear), so the first few range trips, I thought that may have been a factor.
Just spraying in more CLP will usually help for a while, but seems more like a band-aid than a fix for the root cause. (side note: CLP seems to burn off pretty quickly for me, though I don't think it should burn off this quickly...I plan to try a synthetic motor oil next time to see if there is any change).
Last range trip, I fired approximately 60 rounds 100%, then began to short-stroke (bolt closing on empty chamber each time, did not hold open at the end of a mag).
Gas key seems solid, and is well-staked. Buffer tube looks clear; no grime or obstructions. Standard weight carbine buffer and spring are being used. Gas rings seem good.
So that leaves the gas tube and FSB, correct? I haven't yet assembled an upper, so I'm not sure what to look for here. I know the gas port in the barrel could be out of spec or misaligned with the FSB, or there could be a leak somewhere, or the gas tube could be out of alignment with the gas key, but I don't know how to check and confirm these things. The fact that it doesn't malfunction until several-dozen rounds in, is also puzzling to me. Any help would be appreciated.
carrier rail wear
hammer wear