I use a lot of the Cowboy 45 Specials in my 45 Colts, simply because I shoot mostly Cowboy Action Shooting in a Black Powder Cartridge catagory, and they save me a lot of money over the year by using much less powder per shot.
I just never could get happy using fillers in a BP round, and don't need full house 45 colt rounds to hit a steel target a few feet away. I can miss with the C54S round just as easily, for less money, LOL!!!!!
I would guess that's primarly the reason most folks use a shorter cartridge in guns where they are available, for reduced recoil and wear on the guns if shot a lot, and for economy of reloading and shooting. Like 38/357, 44 sp/44 mag, C45S/45colt, the examples are many, and all for valid reasons.
Aprox 26 grns of FFFG APP in a C45S versis aprox 34 grns FFFG APP in a 45 colt, over maybe 5,000 to 10,ooo rds a year makes a big diference in the cost of powder.
Greeenriver