One of the other reviews here summed this up very well: "routine but entertaining B-western with few surprises". It's not going to linger in the mind very long after it's over, but it's pleasant enough to watch while it lasts. It's got a clearly delineated hero and villain and entertaining supporting characters, with the expected brawls and gunfire and impressive rural scenery to take in.
The very stolid George Montgomery plays Cruze, our good guy, who makes the acquaintance of outgoing gambler Fairweather (Frank Faylen, who delivers a nuanced performance, easily the movies' best) while travelling. They arrive in the small town of Marlpine where the mayor (Fay Roope) makes note of Cruzes' fighting abilities and hires Cruze as the towns' marshal. Cruze soon has his hands full dealing with the thuggish Moran gang, a bunch of cattle rustlers led by beefy Tray Moran (Neville Brand, a good antagonist). Cruze falls for local cattle rancher Charlotte Downing (pretty Dorothy Malone) while the amiable Fairweather ends up accused of murder.
As directed by Ray Nazarro, a Western veteran whose career dated back to the silent era, "The Lone Gun" is really no great shakes but its story is easy enough to follow and reasonably enjoyable. Watching some of the actors at work is really the main attraction; also appearing are Skip Homeier as Cass, Charlottes' morally compromised but not really bad brother, Douglas Kennedy and Robert J. Wilke as members of the Moran gang, and Douglas Fowley as the sleazy bartender.
One good thing about these older movies is their often brief running times; for example, this only runs 75 minutes. They very much get to the point and don't waste time. The wrap up is quick and satisfying.
Overall, a fine diversion.
Six out of 10.