I use a couple gas checks to make mine. I seat one gas check "cup-up" over the powder and then fill with #12 shot, seat the second one "cup-down" over the shot, and apply a moderate crimp. I prefer #12 because it really creates a "cloud" of shot that ensures multiple hits to the nervous system, and instant incapacitation. I have shot a couple big diamondbacks and one behemoth cottonmouth with these loads, and it stopped the snakes better than anything I've witnessed before. Most snakes writhe and twist after death, but these just went still. The distances ranged from three yards to about seven yards.
FWIW, I have used factory Speer loads, and was less impressed with the performance of the #9 shot loads, although the 22 Mag loads performed well, and they are loaded with #12.