Not entirely sure but each load will be a little different like i was shooting sellier and bellot #4 buck 27 pellot at least for me anything past 15 yards could not really call anything a pattern. With Federal OO buck LE 9 pellet flight control took out to about 35 yards before i had the same result as sellier and bellot. slugs my m1 i know different model but same idea elevation was on at about 50 yards but was about 4 inches left with just smooth barrel. The slugs were federal trueball.
I picked up a used M1 that didn't look like it had been shot much at all it is 16 years old when i got it about a year ago. Haven't shot it much the last time i cleaned it noticed a couple very small slivers that were magnetic mostly around where the recoil spring cup is not sure if its from break in even given the age the only wear i can see is where the bolt rides on the barrel on its way to lock up and a little bit on the feed ramp. Just wanted to get some ideas so far have put maybe 120 rounds of mixed ammo threw it cycles everything even the next to no brass bird shot.