Aut cum scuto aut in scuto
Bore obstruction, I'd bet. Probably rammed the barrel into the dirt and didn't realize it.
Enough mud on the exterior of the muzzle end of the barrel to support your theory.
It also looks like all of the rifling is gone as well.
Those are smoothbore from the factory.
Not an Abrams: looks like a T-72
Now if it had been in the U.S. Army, there'd be a master gunner doing a classic 'face palm' and repeating "WHY me?"
Looks like a Eastern block uniform on the crewman? on the left side of the picture