With the Marlin, the ctg. is fed at an angle. Thus, there has to be some chamber tolerance with those type actions for smooth cycling. The '66/'73 clones feed straight in from the elevator and the chambers can be tighter than angle feed lever guns.
The .44-40 is a thin walled case designed for lever guns. The .45 Colt is a thick walled case. With cowboy action, low powered loads, the .45 Colt is bad about blow back. The thick walled case won't expand enough with those loads to seal itself against the chamber wall. .44-40's will seal with most any load.
The .45 Colt is straight walled and easier to reload. The bottle neck, thin wall .44-40 case will crush if not handled with care. You gotta bell the case mouth slightly to receive a bullet.
I turned my .45 Marlin Cowboy into a 'diller killer. With 300 gr. cast or jacketed bullets ahead of a full house 4227 load, that gun is a real killing machine. I installed a Bushnell Holosight, really neat. No blow back here...
For CAS, I went with '73 clones and .38 Spec.
DF
