AviD
I have patterned 3 differnet guns with about 15 different loads, my results show some definate rules.
Browning guns have factory lenghtened forcing cones and invector plus bore dia. is .740
Gave the most even and densest patterns I've shot
Benelli M-2 with 3" lenghtened forcing cone gave lots better patterns than the factory forcing cone.
old sears Aya S/S choked mod & Full--- MOD bbl. gives better patterns than FULL choke bbl at 40 yards, note this gun also has lenghtened forcing cone.
Other rules of thumb I follow, no loads over 1 5/8 oz.
no loads over 1300 fps----what I have found when I step over these self imposed rules my patterns are blown, which I think is following general rules of shotgunning.
Remeber shell manufactures are selling shells and with the cost today not very many people do intensive patterning just go hunting
