Last year I built these AR's: AR-15 Picture Thread | Page 13 | Survival Forums So, I build the rifles, take 'em out and shoot a few mags through them and everything is hunky dory. I make a few notes about changes I would make if I did it over again (maybe one size lighter barrel profile so I could use a lighter butt stock for balance, skip the BAD levers (still undecided), maybe skip the anti-roll pins for easier field maintenance, blah, blah, blah. Overall, I'm satisfied and happy. I'm getting ready to work up a defensive load based on the Nosler Bonded Performance, and I've bought a fair amount of XM-197 and M855 for practice that also generates brass for the new loads, and I need some brass. Last weekend I decide to generate a bit of said brass and decide to test rapid fire with some mixed loads, so 2x30 round mags of XM-193, 2x30 round mags of M-855, and 2x30 round mags alternating each round. Only a dozen mags total, so not a huge test. I'm at a childhood hunting camp I recently located, and somebody left a can, a suspected terrorist can, about 50 yards away where there is a nice 200' backstop. The can is dancing all over the place as fast as I can pull the trigger, has denounced Allah, and has asked for a bacon sandwich. Rifle number 2 gets through the first two mags, then 7 rounds into the M-855 I get a FTF. I recharge, fire it, and another FTF. I pull the mag and when I check to make sure the chamber is clear I see that the bolt is forward of where I expect. It turns out that the buffer has escaped the retaining pin. I play with it and sure enough I can replicate the problem manually. I use the remaining mags in rifle number 1 to keep that can in its place (pretty much disintegrated). The buffer tube in this rifle had a slight manufacturing error which I thought I had corrected when I built the rifles. The front portion had been cut at a very slight offset, so that when I tried to join the upper to the lower, the top of the buffer tube interfered. I simply filed a small amount away and made sure that the buffer would stay captive. It did, until it got just enough wear that it failed. A new buffer tube has now replaced it after close examination and very soon it will be tested to make sure it won't let me down when I need it the most. My point is not so much about AR's, firearms, or even equipment. It's about being able to rely on anything you intend to depend upon whether it be equipment, processes or even people. Something I haven't paid as much attention to as I should.