A lot of .22 barrels are made of lower grade steel and shooting large quantities of the shorter (shorts,longs) ammunition can damage the chamber. I have come across older .22's that have a "ring" burned and pitted into the chamber where the shorter .22 case ends. This makes extraction hard when the owner goes back to using .22 long Rifle ammunition because the brass of the case gets caught in the pitted area. Sometimes this ring is only a carbon build up and can be removed, but other times it is actually burned into the chamber. I have no idea how much shooting of the shorter ammunition causes this , but would imagine it would take a lot.