Theoretically the crimp will cause a minor and temporary increase in chamber pressure as the crimp unfolds but wonder if this is enough of a reality to make any difference in pressure, velocity or pattern.
Dave Myrick
True, the difference may be slight, but there would be a difference. A more significant difference would be related to over bore sized wads pressing through a forcing cone. Something that is entirely unrelated when comparing to a muzzleloader.
Many early breech loading shotguns took thin walled brass hulls which were designed to be loaded with larger than bore sized wads in them. i.e. 11 gauge wads in a 12 gauge gun or 9 gauge wads in a 10 gauge gun. There would certainly be a difference in pressures, with everything else being equal, between a muzzleloader and breechloader with those loads.
Having said all that, I am not saying those difference are dangerous or even significant. Just pointing out there would certainly be differences between the two guns relating to pressure.
