I know that basic questions sometimes get ignored here by the cognoscenti but am hoping someone will take pity on a guy not steeped in all-things-doubles and answer a simple question.

Since it's OK to shoot 2.75-inch shells in a gun with 3-inch chambers, I'm thinking it must be OK to shoot 2.5-inch (vintager-type) shells in a gun with 2.75-inch chambers. Yes? No? Or ... ?

Pete