For what it's worth I found this.

His pistol was a S&W model 26 chambered in 357 Magnum, 4 1/2 inch barrel Stanless Steel, wood grips.
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What? The model 26 was a 6-1/2" light barrel in .45 ACP.

Eastwood's gun in Gauntlet was most likely a Model 66 with 2-1/2" barrel.
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The revolver is a nickel N frame Smith. The film predates the first stainless N frames by a year or so, and the 3 or 3.5" barrel on it wasn't offered in a stainless S&W until much later in the 80's.

You can disqualify either a M27 or a M28 from the list of possible candidates because they had tapered barrels on them. So this is not a .357. It isn't a M66, either, because those are based on the much smaller K frame.

That leaves the M24 in .44 Special, the M25 in .45 Colt, and the M29 in .44 Mag. The question is was this handgun a factory gun or was it a Lew Horton special?

If we decide it was a Lew Horton gun, it could be any one of the three listed.

If we agree that it is a factory gun, then most likely it is a M24. I will guess that it is factory as most of the large frame, short barreled Lew Horton's were using a round butt instead of a square butt like the one in the movie.

In any event, whatever the chambering on the revolver is, it is not a common handgun you will find. The 3" and 3.5" N frames never were made in big numbers like 4", 6", 6.5", and 8 3/8" models. Lew Horton's are more common than the factory offerings, and those are still hard to come across. If you have one, consider yourself lucky, I've been looking for a M24 with a short tube for years and I haven't come across one for sale yet.
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I think you're off.

The Lew Horton 3" 24s were blue, not nickel, and were made in '83. The stainless shorty 624s were made far too late for this movie (c. 1985, per Standard Catalog of Smith and Wesson, 3rd ed.).

A nickel M27 seems possible, since they were factory-offered in 3.5" barrels, and the factory 3.5" gun was offered until 1979. Nickel anything seems like a weird choice, though, for cop from Phoenix. I mean, how much rust are you gonna get there?

I don't think its too small for a K-frame gun, either; I also like it as a 66 from an appearance perspective.
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Caveat venditor.