After I shoot these .45 Colt loads, I'm going to try .44 magnum, to be shot in a S&W 629.
The IMR website lists a 22.0gr charge of IMR4227 for a 240gr JHC 44 Magnum with a 'C' footnote, meaning a compressed charge. From what I've found on the web, this appears just to mean that the bullet is seated directly on the powder, with no intervening air space like the 45 Colt load.
Is there anything to watch out for here? How much compression is enough?