There is no minimum requirement I know of except power factor 125, but that is for ammo shot in a 4" barrel, not your actual gun if shorter. So a 2.5" M19 is legit. The short extractor rod and short sight radius will hamper you a bit, but it is your choice. I know people who have shot with them and with 3" M13 and 2 3/4" GP100, so it can be done.
Holster requirements are the same for revolver as auto; and there are specific requirements for speedloader carriers. Just do as I do and buy RTP:
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