The O.P. wrote he was talking Fox 16s most of them made for 2 9/16 shells and with chambers 2 7/16 or even shorter. One of such with very short 2 3/8 chamber has 3/8 lap over if using 2 3/4 shells. The tests often referred to were done using 12 ga and 1/8 lap over but many don't know or dismiss those boundaries and try to apply to Fox 16s and also to 20s sometimes chambered very short like 2 1/4 inch. That fox 12 gauge & 2 5/8 chamber test doesn't fit. All things equal tighten the restriction ahead of a shotgun shell with x pressure and that pressure increases in proportion along with velocity and recoil in that gun.
