Originally Posted by Hossbreed44
When shopping for a .45ACP Blackhawk extra cylinder for an 1971 OM 3-screw .45 LC Blackhawk, will a NEW MODEL cylinder work?
Are the cylinders the same between OM and NM?
The short answer is Yes.
The long answer is:
OM 45 cyls are all for the large frame.
NM 45 cyls for the standard Blackhawks, not the NM flat Top 45 blackhawks, are all for the large frame, therefore the same size as the OMs.
They will interchange. With rare exceptions, the timing will be fine (see KidVermin's comment above).
As with all cyl swaps, it's only the overall length that can vary a bit and may need fitting: at the front gas ring and possibly the barrel to cyl gap.
Measure you 45 Colt cyl and shop for the same overall length or a bit longer ACP cyl.