Colt Expanse Kaboom

[call_me_ski]

This happened at a range that I used to work at. I am posting this for Polishmike while he waits for his account to be activated as he is interested to hear what you guys think.

This is our rental 2016 Colt Expanse (pre forward assist) carbine. It had 10-12k through it. Normal cleaning was done a couple K ago. Our manager reported to the range to assist a customer with a failure. With the new California mag locks this is a lot harder than it should be. After clearing the failure, he had another failure to fire. He racked a new round in and it went kaboom. Video can be seen here: https://youtu.be/-KJq23shaTc He had multiple facial lacerations but was treated and released without any long term damage. Reminder: Always wear eye pro.

Here is the complete disassembly:

Carbine as it left the range. Most of the upper and BCG parts were found but the extractor is MIA.


First check is for barrel obstructions. None found.


Close up of the carnage.


Reverse side. Note that the bolt catch was sheared off.


The underside after being removed from the lower. Note that the bolt is still locked in. This was not an OOB in my opinion.


Another view.


The upper receiver completely disconnected from the barrel extension.


No barrel bulges. Not a squib IMO.


The rest of the case in the chamber.


Lower checks out fine besides the bolt release paddle not being there.


A look inside the upper receiver after removing the barrel.


Another view.


Carnage.

[call_me_ski]

Where the upper disconnected.


Using PTG Go/NoGO gauges on a new bolt with ejector removed.


Go closes fine.


No-Go will not close. Headspace is in spec IMO.


BCG out of the upper


Another view.


Bolt with whats left of the case head.


Case head fell out easily. Bolt cracked all the way down.


View of bolt


Bolt and cam pin out.


Case head 1


Case head 2


Case head 3 Note the imprint of the ejector.

Before anyone says 300blk – here is the case I pulled out


Next to a new round


Ammo box


The rest of the ammo


Aimpoint ACO lens cracked


But it still works.


Barrel after removing extension. Measured with calipers and chucked it up in the lathe and used a dial indicator and couldn’t find a bulge.

Conclusion:

The way I see it this could have been one of two things. One guess is bad ammo. I strongly doubt this as these weren’t Grandpa’s reloads. Not to say that factory ammo is always perfect but AE lake city stuff is usually spot on. Double charges are impossible because of the volume of powder and I just don’t see half a grain too much powder causing this spectacular of a failure. I’ve seen ejectors warp with 10% over rounds but nothing like this. The lot number on this ammo is: SMQ16L836-002

My second guess is a bolt failure. We have had a few bolts break at the cam pin point and that is pretty common. Not a big deal. New bolt and go. This would have had to be an extremely poorly made bolt and would have had to developed some internal cracks before this. This is a factory Colt bolt and the MPI markings are still visible.

I am sure someone with more experience will chime in and provide their theory. I am open to hearing it and can provide detailed pictures of anything.

[Iraqgunz]

Are those gages marked 5.56 or .223?

[officerX]

Yikes!

[BFS]

Specifics on the initial failure, and the type of California compliant hardware installed?

[call_me_ski]

Are those gages marked 5.56 or .223?

.223

The only modification of the rifle is a California complaint magazine lock.

[bmfdez]

CA mag lock makes clearing malfunctions more complicated. Especially double feed, and not being able to drop the mag and etc. Have heard of incidents when trying to clear a double feed.

I initially thought that was the case. Since it was said he had a malfunction, racked and put in a new round then went Kaboom. But, from the video, I dont think that was the case. Look like he malfunctioned, cleared it, then did something weird that we can't see, then fired again and that's when it went Kaboom.

Also interested to see if experts will chime in with a reasonable explanation.

[Kdubya]

Tagged for building my KB knowledge base. Definitely an interesting one. That ammo is fairly new to the Federal lineup, right? Wasn't there also an issue with one of their 55gr loads previously?

Compared to other KBs I've seen, that upper doesn't look to have contained it all that well. Then again, it's hard to make that assertion without knowing the true cause of the KB. Glad to hear no serious injuries were sustained.

[fallenromeo]

Dang, that's quite a blow up. I am very interested to hear what some of the experts have to say about what could have been the problem, based on the pictures.

[Todd.K]

Typical KB with a bit more than average damage.

Caused by excessive pressure. As the case turns liquid the pressure takes the path of least resistance on the bolt head, the extractor cutout. This can split the bolt carrier (and sometimes the barrel extension) and that leads to the upper splitting apart.

OOB is ruled out by the amount of damage.

If barrel obstruction is ruled out you have to ask what was different this time vs the last time it fired normally. The answer is what was in the chamber.