CW, I like your style! I've used Unique and 2 gaschecks in my 45Colt and my 41Mag, BUT, contrary to what has been posted, my best luck on grouse has been with #4 shot - and out to about 15 yards. My longest shot was out of a 6" 357Mag with the Speer factory shotshell and it did amaze me.
A while back, I was playing with 30-30 cases cut back to cylinder length for the 41mag and 444 cases cut back to cylinder length for the 45Colt. Never got to any real world testing, other than to know they went bang and pop cans were jumping down range. They are a bit of a pain to build, but with nothing but time, they are fun and I believe a bit more effective than using standard case length. I used the Speer published data for shotshells in all cases. It was plenty, at least for me and the grouse. Never had to do in a snake.
Regards,
Sweetwater