I have no information on this other than what you see in the pics. I’m thinking a possible overload is to blame.

Possible over load or maybe a bullet stuck in barrel ,wrong powder ?

well my guess is the think is poked...plain n simply poked.....time to buy a new one....

Now THAT takes talent.
Special school type talent, but talent never the less.
Seriously I can think of at least 3 things that might contribute to this, 4 if the owner is a moron.

Bolt lugs look OK as does the barrel, so I can't see it being overpressure.
Possibly the bolt not quite fully rotated into battery.
Trodden on when propped up, fallen with or run over would be my guess.

English Mike wrote:

Bolt lugs look OK as does the barrel, so I can't see it being overpressure. Possibly the bolt not quite fully rotated into battery. Trodden on when propped up, fallen with or run over would be my guess.

Either way, it was DEFINITELY cracked around that area before it was fired.

-DallanC

The upper is well used, abused, and worn out. I'm with Elvis, this was "poked" to many time with the gas piston. Should have stayed with direct impingement as the rifle was originally designed to operate.

So out of the MILLIONS of AR 15 platforms in use, how many have failed like this?

first I have seen, but notice that it is not a mil-spec upper receiver.

No, but it separated at the threads on the upper receiver. I don't see a radius cut at the end of the threads. If you were going to see a fracture that is the exact place.
Also, bear in mind that aluminum has a limited number of cycles before fatigue failures happen. There is no aluminum alloy that can get past that weakness in aluminum.

I would have to concur with the upper failing from metal fatigue and there almost appears to me to be a question on the timing of this rifle as there is a consistent amount of burnt powder on the chamber end and the push rod which would lead me to believe that there is a greater amount gas blow by on the push rod. I base this on having a good deal of experience with the FN LAR//Cdn FN C1A1 which has a push rod and a gas adjustment also 1-9 setting and reverse for grenade launching. I would be interested in seeing the gas block and ammunition fired /loaded for this HK.

Paul...You want to edit that? Just askin'...

Thanks Bushy, I'll leave it like it is for now. (allow alloy nearly the same thing)

I hear jb weld is pretty good stuff