Shotgun ammo may used in a chamber LONGER than the shell, but not SHORTER...

So a 3.5" chamber would safely shoot 2 3/4, 3 or 3.5 inch shells, but not vice versa.

Shotgun chambers are tapered..There is no sharp shoulder for a projectile to "catch" on.. You can safely shoot 2 3/4" inch slugs through your 3" chamber, as long as you are not trying to shoot them through a supertight turkey choke or some other choke mot recommended for slugs..