Images Journal calls it "one of the wildest and most exciting Westerns of the 1950s." Slant Magazine describes it as "a magnificent B western". Rotten Tomatoes has a critics score of 100%.
Senses of Cinema concludes,
Forty Guns is an exemplary film in many ways. It reveals a filmmaker ahead of his time who pioneered techniques which were appropriated by acclaimed art movie directors while Fuller himself is still regarded as a B-movie director. Fuller’s comments on violence and politics in American society are stated subtly within the image, never didactically bombarding the audience into insensibility but leaving them to consider the implications for themselves. ...