The gun in question in this movie is repeatedly called a "Colt Wesson .44". There are Colt guns and Smith & Wesson guns but there is no such thing as a Colt Wesson.
McDonald Carey sings the song at the end. He was musically trained.
Actually, the characters in the movie are calling the gun in question a "Colt Western .44", not a "Colt Wesson .44". Not only is there no such thing as a "Colt Wesson .44", but Colt never formally applied the term "Colt Western .44" to any gun which they ever manufactured.