The most common cause of a barrel failure other than an improper load for that barrel is a barrel obstruction. Virtually all barrel bursts are barrel obstructions. This can be snow or dirt or insects, etc plugging or partially plugging a barrel. It can also be a "puff" load caused by oil in the powder, partially blocked powder column in the reloader, or any number of ways a reduced load or powder problem causes the wad, part of the shell case, or shot to stay in the barrel. It can also be caused by certain powder being very cold causing improper ignition.

Most hewre do know what a proof load is but there are some who may not. A proof load is a carefully calibrated load shot through each barrel after exactly measurements are made on each barrel. After the firing of the proof load, the measurements are made again. ANY increase in these measurements means that the barrel material has undergone a plastic deformation and this means the yield strength has been exceeded. The gun has failed proof test even if no overt damage has resulted. Now Joe out in his back yard putting an old shotgun in a tire and firing a very heavy reload in it accomplishes absolutely NOTHING. There may be plastic deformation that he does not see (meaning small or large damage to the barrel), or his load was not very hot after all and the gun may not be up to a full proof load. Don't try this at home.

Pete Hiatt, engineer