A firm taper crimp isn't necessary, in fact it's prolly part of your problem.
If your bullet has a crimp groove then maybe if you use a roll crimp die in the correct size, then a firm crimp would help.
Overcrimping is easy to do, esp with soft bullets.
A couple more questions....
With no moonclips, do your rounds seat flush, or fall below flush?
If they fall through and stop at the end of the chamber, then you got a 625 chambered in .45 colt.
If the bullets seat and look just like they would if you have the moonclip, then it's ok, and it's the right caliber.
I'm not just a gun.
I'm YOUR gun.