Bolt failure not resulting in Kaboom

[rero360]

I just returned home from completing the Squad Designated Marksman course at Camp Robinson, AR and saw an interesting failure.

This happened on the other firing line, I was working in the pits at the time. The other soldier reports that he didn't notice anything wrong with his rifle (M16A4) at the time, didn't realize it until we got back to barracks at the end of the day and was cleaning weapons. I am figuring it gave way on the very last round he fired that day.

http://i26.photobucket.com/albums/c101/rero360/20130205_191523_zps1b44dd65.jpg

http://i26.photobucket.com/albums/c101/rero360/20130205_191547_zps11e59a18.jpg

http://i26.photobucket.com/albums/c101/rero360/20130205_191613_zpsde1b3edb.jpg

As you can see, the other lug opposite of the extractor is badly cracked as well and probably only a round or two away from failure. The next day he found the broke off lug laying at the 600 yard firing point where he finished the day at. We were starting at the 100 yard line and working back 100 yards at a time getting our windage and elevation for irons at the time.

We started the course with 28 students, 22 graduated and I was only one of four who finished the course without a single failing grade on any of the shooting or written evaluations, or the practice evaluations. I think the least number of rounds we fired any given day was around 212 and the total round expenditure was somewhere around 45K for the whole course not counting the 7.62 thru the M14s.

[kaltesherz]

Congrats on passing your SDM course, that was the most fun I ever had at a Military school, that's for sure...

I've never seen a bolt fail, but apparently when they do lose a lug they can still function for a little while longer without the shooter knowing until the break it down for cleaning. IIRC 2 lugs failing is where it gets dicey.

[kmrtnsn]

There is quite a bit of redundancy in the AR bolt lug design. As long as the bolt can lock in place and be retained in a locked position during the firing cycle, there will not be a "kaboom". It is when the bolt fails in a manner that it cannot maintain its locked position during the firing cycle is when ugly things can happen.

[sinlessorrow]

Any idea on ammo used and round count on that bolt?

[rero360]

Yeah, it was for sure a really fun course, a lot less stressful to me than JFO (that one caused a few additional greys haha)

I don't know the round count on that bolt, but I'd be confident in assuming it was all M855. The rifles definitely showed a lot of wear, the instructors said they rebarrel them about once a year, figure 10 to 11 classes a year, average round count of 1,800 to 2,000 per class. I know those rifles see a lot of use, and abuse to a degree, I discovered the KAC RAS on my rifle was broken inside of the slip ring. Not that it really mattered as I didn't use it for anything and did all my shooting from mag on the ground or jamming my knee in between the mag and pistol grip for kneeling shooting (which I hated due to still fractured ankle and getting hot brass down my top costing me the last two rounds of the course of fire) We also experienced one gun that had to swap lowers due to the trigger going south (guy said it felt almost like a stock M&P trigger, really mushy)

We also got to field the school house's brand new Bushnell spotters, I almost immediately broke one of the legs on mine's tripod. They new going in that they were kind of cheap and were looking for different tripods for the scopes.

[Razorhunter]

Is that an FN bolt? I've never seen a bolt stamped MPE.

[Ned Christiansen]

That is 100% typical if that type of failure. First one and then other lug adjacent to the extractor goes. That crack and break line, if you could precisely measure 10 bolts with this failure, probably would not vary .005 from bolt to bolt.

[nanners83]

Is that an FN bolt? I've never seen a bolt stamped MPE.

That's an underlined F. Looks like most bolts I've seen in issued rifles.

[sinlessorrow]

Yeah, it was for sure a really fun course, a lot less stressful to me than JFO (that one caused a few additional greys haha)

I don't know the round count on that bolt, but I'd be confident in assuming it was all M855. The rifles definitely showed a lot of wear, the instructors said they rebarrel them about once a year, figure 10 to 11 classes a year, average round count of 1,800 to 2,000 per class. I know those rifles see a lot of use, and abuse to a degree, I discovered the KAC RAS on my rifle was broken inside of the slip ring. Not that it really mattered as I didn't use it for anything and did all my shooting from mag on the ground or jamming my knee in between the mag and pistol grip for kneeling shooting (which I hated due to still fractured ankle and getting hot brass down my top costing me the last two rounds of the course of fire) We also experienced one gun that had to swap lowers due to the trigger going south (guy said it felt almost like a stock M&P trigger, really mushy)

We also got to field the school house's brand new Bushnell spotters, I almost immediately broke one of the legs on mine's tripod. They new going in that they were kind of cheap and were looking for different tripods for the scopes.

Sounds about right then, just an old bolt. That is where the vast majority give way.