It's been proven many times, by actual pressure-testing, that firing 2-3/4" ammo in chambers as short as 2-1/2" doesn't raise pressures. It has nothing to do with "how the maker bored the shotgun barrel." But this myth continues to wander along.
The only possible problem is modern ammo loaded to higher pressures than old guns can handle. But it has nothing to do with whether the chamber is 2-1/2" or 2.59".
