I need to correct a statement I made earlier about interchangeability of pistols within a single holster; in fact it is the Commander (or M39) that fits S&W 4" N frame holsters (I had said Government model, in which case it would be the 5" N frame).
I bought this Bluemel specifically for the purpose, of asking my co-author John Witty to photograph this holster, or another, using real pistols.
Worked this out early '70s, quite by accident, messing around (they called it work but I would work all day then stay late; then go home and forget my paycheck and have no money all weekend) with an M39 in a Border Patrol holster for the M29. Remember LEOs didn't use autos at all then (one department here, another there, doesn't really count) so this was all new to us.
Anyway, as these pics the two pistols fit into the identical holster without any changes including the safety strap. Yup, there is grip interference on the auto, at the knuckle of the second finger; but the Bianchi revolver holster was/is relieved there (for a surprising set of reasons).
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One would have problems with the mag button's clearance if done with this particular Bluemel holster because there is not metal inside the shank, and so the shank can't be bent away from the button. A relief could have been cut into it; or a 'well' as done on Sessums holsters; or a second welt as done on Myres holsters; point is, don't do this at home, kids, unless you're watching for your mag button.
I suppose the point of mentioning this at all, is to say that if holster designers were really paying attention back in the day they were using the same pattern except -- back in the day the trigger of the auto was expected to be exposed; in which case cutting out a 'U' relief over it was the solution. This essentially is what was done on the Brill though it appears N.J. did it the hard way anyway.