Are the colt 45 and the 45 long colt interchangable?

no with regard to cases. 45 long colt has a ridge that sets on end of cylinder. 45 acp is rimless. however, they do make a cylinder for the acp that can be used on colt single actions. i have just bought a uberti 45 and was told by the dealer "a very reputable" that a 45 colt, and a 45 long colt are exactly the same. it's when you add the acp that it is a shorter round with no lip on the back of the case where the primer fits to stop it from going all in the cylinder