Hammer:
This article written by one of our long-time forum members is the absolute best quick reference on frames and sizes available. I bookmarked it and find myself referring to it all the time when I get a little fuzzy on sizes.
Like the OM 44 the other large frame OMs (45, 41, and 30 Carbine) will have recessed case heads.. The 357 does not. Makes it easy to pick out a 357 OM on the far side on the display case.