Bushmaster Jammed Bolt


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koja48
July 22, 2007, 09:54 PM
Had a round bind-up the bolt on my AR today. Didn’t attempt to fire because the slam of the action didn’t sound quite right when it closed (plus, I was checking both the mag-fed round & the one below it in the magazine for bullet movement between shots). Ejected it with some difficulty, measured OAL – dead-on. Disassembled rifle, bolt, examined & cleaned same (had only put 15-20 rounds thru since last complete strip-down & cleaning). No revelations there. Reassembled, loaded another from the same batch of 4 ), with the same results (only change between this work-up batch & the previous 3 batches was a slightly increased powder charge @ 0.2 grains at a time and NO indications of excess pressure during the previous firings, plus I weighed EVERY charge). The round ejected with some difficulty.

Tried the same length OAL rounds I had been using previously & it functioned flawlessly – same brass, same CCI 41 primers, same Hornady 50 grain ballistic tips, same Remington 1-fire brass (all brass at or below 1.760 in length prior to priming & charging) identical seating depths (bullets, primers). Neck ODs were identical.

When I got home, I re-measured; after I pulled bullets, I discovered the 2 that jammed were significantly longer than the rest in that box. Resized the 2 cases & reseated the bullets as dummy rounds; same results. Seated them a few thousandths deeper, loaded them in the magazine & everything worked fine (Redding full-length resizer & competition seating die).

The only conclusion I can draw is that since I had seated all 4 batches used today not as deeply as my old loads to decrease bullet jump (these were at 2.258 COL & OAL was well within the 1.903 chamber length of the rifle), the “extra” length of the bullets created a slightly greater COL & didn’t feed from the mag cleanly, & prevented the bolt lugs from fully engaging.

Went back to the range with rounds seated at the new shorter OAL/COL & everything worked without a hitch. On the plus side, being extra-attentive when working-up & shooting new loads pays dividends!

Any theories?

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