With the load you're shooting, don't expect much growth in case length. I shoot 9 gr. Unique with the same bullet and there just isn't much change. You can probably make the case (no pun intended) that you want to extend casemouth life by taper crimping but .45 Colt brass is not that difficult to obtain. As previously posted, taper crimp is designed to prevent bullets from being pushed into the case. Roll crimp is designed to prevent bullet from coming out of the case. IMO, with revolver ammunition suggest you use the roll crimp just like factory ammunition. Just my dos centavos, YMMV.I am shooting a 255 grain cast bullet in a Ruger .45 Blackhawk at fairly low velocity. I am using 8 gr. Unique. Don't do any formal shooting with it, just plinking. Thought I would not have to be so picky with case length if I taper crimped.
I believe the American Rifleman once tested both the roll vs. taper crimp in .45 ACP to determine which gives the better accuracy. For the life of me, I cannot recall which one came out on top, however, loads which give a one hole group from a Ransom rest do not necessarily look the same when fired one-handed during the rapid fire stage of bullseye shooting at Camp Perry. My wobble area alone would negate any super accurate ammunition I could possiby load. My point being that we can pursue accuracy to the nth degree but at some point, other factors come into play.I am reminded of a past exchange with William Iorg in which he reminded me that old time bullseye shooters used roll crimps for best accuracy from the .45 ACP in the 1911. . . The taper crimp was popularized solely on the proposition that it extends case life (which it does; I've had up to 50 load out .45 ACP cases taper crimped . . .