You might want to look for 5 in 1 shells. They are used by the movie industry and I think that 45 colt is one of the guns they are intended for, but you would have to check. They are basically a 38-40 blank as I recall and because of the low pressure were used in 38-40, 44-40, 45 colt and a couple of other calibers.
cheers mooncoon