Really hard to tell, but my first impression is that a shell in the magazine was set off and may have set the one being chambered off before the bolt was completely locked.
The area where the magazine tube was is completely burned and the barrel shroud is separated/sheard from the barrel tube itself and driven upwards splitting the receiver. No buldge or split in the barrel is evident as would be likely from an obstruction of anykind.
Could be a combination of factors, including overload when handloads are involved.
Looks like a Remington M11 but it makes no difference.

Ithaca M37 have been known detonate a shell cycling out of the magazine tube also. The last one I saw destruct in that manner, the shooter lost part of his left hand.
Just my guess.