Interesting failure
I have seen lots of different failures of parts over the years, but this is a first for me in 20 plus years of military M-16/M4 use and another 15 of civilian AR-15 use.
Yesterday, I was exercising a clean and properly lubed mid-length 16" 5.56 chambered (verified) carbine mounted with Luepold VX-R Patrol optics with a Spike's Tactical lower with their Nickel-Boron single stage trigger. I had just swapped out the buffer to a slightly heavier Spikes T2 (it had an unmarked CAR buffer previously) as I was having a very sporadic issue with the bolt not locking back on the last round with 5.56 rounds (not .223) prior to the swap. The gun (except for the buffer) had close to 1000 rounds through it, with 500 being Federal AE .223 and the balance 5.56 XM193.
I had a mixed stack of twenty-two 20 round mags by C-products and Brownells, each loaded with 1 round of 5.56 XM193. After the 3d shot (bolt locking back each time) and with a new mag in and bolt released, I squeezed the trigger and felt it wasn't reset properly. When I released the pressure it reset and I sqeezed again and it functioned. After the "what now" thought of a problem with the buffer, quickly dispelled as the bolt had locked back previously, I thought of fouling in the trigger mechanism of some type. I cleared the weapon, broke it open on the line and moved back to a bench with the lower to look at it with my tools/gear back on the bench.
I found that the Hammer pin had sheared in half at the inner groove and only the left half of the pin was still in place in the gun. I replaced the pin with a spare from a repair kit I keep in my range bag.
Casual visual inspection of the pin showed no flaws other than it was a clean break. By happenstance, a group of 20-30 Federal Marshals and IRS agents were doing quarterly training and a couple of the Marshals with whom I had casual acquaintance came over to look at what I was doing. They had one of their fellows, a trained armorer, come over to take a look at the pin. While I had never seen that type of failure, he told me that they had a single M4 Colt that has had 3 hammer pin failures (!!!!!!!!!) like that, but he had seen no others of that type.
Out of concern, I fired another 240 rounds, 44 single round per mag and the balance full mags, out of it after replacing the pin with no further malfunctions of any kind and the bolt locked back each time it was supposed to.
What did I learn (or reinforce that I already knew)......well, it pays to always carry repair parts of all types with you. It also pays to carry extra rounds so that if you have a failure and repair on site, you can exercise the gun right then and there to see if it functions and is reliable afterwards.
Other than that, failures happen, but it was the first hammer pin failure I have seen.
Last edited by Chorizo; 03-23-13 at 16:23.
USMC, 21 years and 21 days. But who was counting?
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