Some of the old barrels were "backbored" from the factory, though the backbore ended before the area where the choke tube begins.
What constriction you'd end up with is a moot point; performance is what counts and the step in the bore did not quite act like an additional amount of choke.
I used a regular modified choke tube in mine (backbore, step-bore 870TC), Carlson's brand, with good performance from 16 yards on back.
If you're getting indifferent performance, check it on a pattern plate to give some idea of how much choke you're actually getting.
Regards, GAP
What constriction you'd end up with is a moot point; performance is what counts and the step in the bore did not quite act like an additional amount of choke.
I used a regular modified choke tube in mine (backbore, step-bore 870TC), Carlson's brand, with good performance from 16 yards on back.
If you're getting indifferent performance, check it on a pattern plate to give some idea of how much choke you're actually getting.
Regards, GAP
