That is probably too much constriction. I wouldn't risk it just because an error would lead to a situation that is basically unfixable.
I have shot remington slugs through a few 16ga cape guns and with the foster design there never seemed to be any issues around them squeezing down.
Surprisingly enough, they tended to be fairly accurate and regulate ok as well in the guns I shot them in.
The fired rem cases are inbetween 2 3/4 and 2 5/8.

Tom

Carbonation without fermentation is tyranny