Armbar,

I don't modify my load down at all - what I do avoid if possible
and definately at the range when practising is firing round after round
and getting the barrels / barrel metal hot - after all, more wear is caused
when the barrels metal is hot.

In hunting DG there is not much you can do about it.

I don't think you or I will ever wear out a DR and I shoot a fair number
of rounds.

Worn barrels are not a major problem unless the rifling has gone completely.
On older English guns, because of cordite you often see wear and dark grooves
in the barrel but what I look for is that the rifling is still there AND that the
last half of the rifling is good as this is more important.

DUGABOY1 is correct about more wear being caused by cleaning and
not looking after the gun.

500 Nitro