https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=365499
From
https://www.shotgunworld.com/threads/roll-crimping-discussion.522040/
but not a study of 2 1/2" roll vs. 2 3/4" star
I loaded up 6 each of the same load, one roll crimped, one fold crimped and sent them to Precision for ballistic testing.
Federal hulls, 19 grains of Unique, GU1621 wad, and an ounce of #8's
Fold crimps averaged 1206 fps and 7373 psi.
Roll crimps averaged 1238 fps and 7475 psi.
There would be very slightly less volume for the initial gas expansion in a 2 1/2" hull, but as Bro. David said if everything else is equal (including the height of the powder/wad/shot) any increase in pressure should be small.
Since one study is better than 1000 'expert' opinions, please consider sending your loads for testing Richard and let us know the results.
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