I copied this verbatim from what appears to be an investigation report. (Couldn't work out how to put a .pdf file into the post.)


During a recent Firearms Instructor Development Course there was an ammunition malfunction. This malfunction resulted in the damage of the Officers personally owned M4. The results of the investigation showed that it was caused by a telescoping round. This occurs when the actual bullet is not crimped properly to the casing and when it is fed from the magazine into the bolt assembly it telescopes backwards, into the casing causing a dramatic increase in pressure. As a result, and out of an abundance of caution, the Training Academy has recalled all practice ammo and encourages officers to regularly inspect the ammunition in the duty magazines. If you have any question please contact Range Master, Officer David Thompson.

We are extremely fortunate that all safety practices were in place at the time of the accident and this prevented the officer and those around him from suffering any injuries.

General

* Officer conducting barricade work, shooting steel at about 65 yards. Officer was using his personally owned rifle, a Rock River M4.

* Officer not injured.

* It is because of these possibilities that we stress proper safety equipment at the range - eyes, ears and ballistic vest, and designate a Medical Staging Point for emergencies.


Why

* Bullet telescoping back into case.

* Loose crimp.

Victim

























Conclusion

Most catastrophic weapon issue I have ever seen in over 30 years of shooting the platform - Paul Howe

End of Report.

These two icons were in the email in which I received the report:



Looks like it may have been a Border Patrol training activity.

A rather nasty accident that had the potential to be much worse. Thankfully nobody appears to have been seriously injured. Can't say the same for the rifle though.

If anybody wants a copy of the .pdf document, send me an email address and I will forward it on to you.

Cheers, Vince

Ouch, luckily nobody was hurt. Remington does have a recall on different lots with that round. Remington Recall

Black Hills ball!

Rem JHP? ....hmmm....pass.

another example of extremely well designed weapon, nobody got hurt!

This here's another reason I shoot "match" (JOTL) loads single shot. Not from the mag (even if they would fit).

I hate it when that happens. Take care...
Joe

Thanks for the information, Vince!

That was a tragic event. I am curious about the "recall of all practice ammo" used at the range. Were they using factory ammo? All the best...
Gil

Don't know Gil, although I would imagine that they were using factory ammo from the look of the box displayed.

Cheers, Vince

I am concerned about the root cause of this serious failure. A web search of AR failures with telescoping rounds turned up nothing. A review of other sites with lots of firearm failures came up empty regarding AR problems. I agree that a round that goes back into the case can dramatically increase pressures. There certainly seems to be a serious problem with either the ammunition, a bore obstruction or some critical firearm failure. We may never know for sure. Take care...
Joe

The more I look at this and wonder if it wasn't something else like wrong type of powder, case failure, bore obstruction. The reason I think this is that how far would the bullet set backwards until it hits the powder, I would assume the factory would load to near 85%-100% density. But to raise pressure that much to kaboom the gun were talking 70,000-80,000psi or more.

Apparently Winchester had a recall on the same ammo back in 2/2011 as LE agency's were blowing up their guns. They never admitted that they used the wrong powder. And again Winchester has another recall in June, what is really odd is they also mention Remington's Bullets being recalled also.

Winchester Recall

Winchester WSF and 748 look alike so what’s the problem ?

That's a pretty scary failure, very lucky the shooter wasn't hurt. I used to only crimp ammo I loaded for my AR, or Mini-14 until I noticed a couple .308's I loaded for hunting had telescoped. The bullet slid back into the case far enough to be noticeable in the ammo box. I pulled the whole bunch, and started crimping everything I load now.

personal opinion only;I have many units in the ar platform-small cal and large,and the only thing that I can believe is that the bore was obstructed.The function of the action is to keep the bolt closed until the bullet is past the gas block,and is to even close the bolt if it is slightly out of battery.Some of the gi loadings for this platform are over 60kpsi,and I can't imagine the proof loadings are only slighly above that.

Joe Boleo wrote:

...I agree that a round that goes back into the case can dramatically increase pressures. There certainly seems to be a serious problem with either the ammunition, a bore obstruction or some critical firearm failure. We may never know for sure. Take care... Joe

I tend to agree Joe. I have fired many thousands of rounds when in the Army, both GI Ball and Aussie made Military Ball, through M16s without anything that came close to a catastrophic failure like that shown. I've had double feeds, failure to feed, hard struck, soft struck, hang fire and failure to extract, but nothing nasty. However, all of that ammo was crimped and had a sealant between the bullet and the case.

The strength of the components used in rifles today is such that it would need massive pressure to split the barrel, blow a hole in the bolt head, split the bolt carrier and blow the side out of the receiver. This accident has done all of this damage. I suppose in one respect that it is testament to the strength of the firearm that it was able to contain this pressure as much as it has.

Was it an obstruction or wrong powder in the round...who knows, and as Joe says, I doubt we even will.

Cheers, Vince

I fail to see how a round could telescope enough to create that kind of pressure? are those projectiles overly long? my 170grn .270 loads are super duper long and I seriously dought that they would create that sort of pressure unless waaay back into the case...unless the bullet went back far enough to let some gas around the edges before it started to more? as you say we may never know.