RE: Mossberg 500 blows up!
Pro-Line, was your friend using a dedicated slug barrel for his 835.
If not the slug could easily get cocked sideways inside the bore and when it got to the choke peeled the barrel.
Remember we are dealing with 46 thousandths of an inch or 3/32nds" of extra diameter in the barrel of an 835. That is huge inside a barrel.