This list is for people whose knowledge of history and film goes back as far as yesterday's breakfast. I would rather suggest the following as "Iconic" (in no particular order) --
Full Auto Competitors:
Gary Cooper's Lewis Gun in For Whom the Bell Tolls.
William Holden's M1917 in The Wild Bunch.
Robert Taylor's Vickers gun in Bataan.
Audie Murphy's MG-42 in To Hell and Back
Audie Murphy's Ma Deuce in To Hell and Back.
Al Pacino's "Leetle Fren" in Scarface.
Edward G. Robinson's Thompson in Little Caesar.
Steve McQueen's BAR in The Sand Pebbles.
Gary Cooper's 1903 Springfield in Sergeant York.
Tom Selleck's Sharps in Quigley Down Under.
John Wayne's Winchester carbine in Stagecoach.
Jimmy Stewart's "Winchester '73."
Daniel Day Lewis' flintlock rifle in Last of the Mohicans.
Edward Fox's custom assassination takedown rifle in The Day of the Jackal.
The Martini-Henry .577-450 rifles in Zulu.
Sean Bean's Baker rifle in Sharpe's Rifles series.
Any M1911 .45 in every Bogart movie ever made.
I'm sure I've missed many. Suggest your own.