The demographic that would instantly think of a rather nasty beer when hearing COLT .45 probably would not be reading this, so we'll assume you know that Colt .45 (also known as The Colt Cousins) was an American Western series which aired on ABC between October 1957 and September 1960.
Dell produced nine issues of the comic (3 under the Four Color numbering). This story is from issue #4, February 1960 and was drawn by John Ushler.
One of the few places you'd see mention of our involvement in Viet Nam before late 1964 was in comic books such as Dell's Jungle War Stories. This story is from issue #5, October 1963. Art is by Maurice Whitman and Vince Colletta. The cover is most likely by Vic Prezio