Newf,

I have used 3" 12 gauge shells in 10-12 2&3/4" Gauge Mates (different company) with no problems. Some 3" shells will expand past the end of the gauge mate but they are seperated easily.

This year I bought a set of 10-12 XL 3&1/2" Gauge Mates which I will trim back to 2&7/8" for my vintage 10's. Most 3" shells are not quite 3" long.

Mark


USMC Retired