I found this on another forum, Marlin Owners, and just wanted to share it here. This is NOT to bash Colt in anyway but to serve as a lesson to always expect the unexpected when shooting.

Here's a link to the whole story on Marlin Owners.
http://www.marlinowners.com/forums/index.php/topic,54654.0.html

A small part of the text;
I switched the ACOG to the Colt and got on the firing line. The drill was firing from the urban prone, weapon side position. We loaded and made ready and I waited for the threat command. When the threat command came I went into the urban prone position and fired. On the second round the upper receiver blew apart. It took a few seconds for me to get oriented and realize what had just happened. I checked to see that there wasn’t another round in the chamber and raised my hand to let Travis know there was a problem.

The 6920 is on its way to Colt Manufacturing for analysis as of this posting. I will certainly post the results of the analysis as well as the resolution when that information is available. I would appreciate it if the wild guesses as to the cause of this failure were withheld until Colt Manufacturing has had a chance to check it out. I will give a few facts that will help to keep the conjecture to a minimum. The barrel was clear before and after the event and the ammo used was factory XM193. I don't know if the brass was ejected, it appeared to be, however, there could have been part of the brass case left in the chamber, I was too busy trying to get back to training to check, then the gun went via FEDEX to Colt before I had the chance to check because I was trying to catch up on all of the work I had neglected while out running and gunning.

A couple of the pics, more at the OP on Marlin Owners.




ETA; a few more pics.


Be careful out there.