In what scene was the M1 Garand rifle shown in Gran Torino? If I recall correctly, the "M1 Rifle" that he brandished while saying "Get off My Lawn" was clearly a plastic movie prop gun.
The M1 was shown in at least 3 scenes in the movie. First was the "Get off my lawn" scene, then the attempted theft of his 1972 Gran Torino were the weapon was fired once in his garage w/ presumably blanks, and the final scene is where Clint Eastwood is describing his Korean War experience with the young man next door, and shows him the M1. The M1 in the NRA museum is a clearly a real vintage M1 that was used, but the display does not say which particular scene(s) it was used in. (To my eyes, the "Get off my lawn" scene appears to have a real M1, but its a low-light scene, so hard to say).
Based on what I have read, is it customary in movie productions to always have at least 2 props of any weapon that is critical to a scene. You have a real example (often firing blanks) for scenes that require live fire or require close-up details, and you typically have one or more lightweight plastic mock-up props that are used for other scenes where it is deemed safer or easier to use. (For example, if the actor is doing stunts you provide them with a lightweight plastic mock-up to reduce possible injuries from carrying a real/heavy firearm). Their is a whole industry around movie props of course...
Somewhere I have a magazine that shows a bunch of 1911s that were used in movies, and I noted that both plastic and real 1911s were often used, depending on the scene. For example, in the famous
Terminator movie with the AMT long slide with Laser sight, both metal and plastic versions of that pistol were used, and the same goes for the two nickel plated, engraved 1911s as seen in the move
Titantic, two were real, and two were plastic mock-ups. (If I find those pics I post one as an example, the details in the mock-up are usually quite realistic).
BTW, one of the more famous screw-ups re weapon props was during the filming of the 1963 James Bond film,
From Russia with Love, when they were doing the official promotional picture shoots with Sean Connery - and they realized that they did not have a Walther PPK pistol for the photo shoot - but the photographer on the set had a
Walther LP 53 air pistol, so that is what was used for the official movie poster. (The long barreled .177mm air pistol was never seen in the movie, but that is what happened with they didn't have the proper movie props for that film).
and here's another picture:
...that particular LP 53 air pistol is apparently in a museum in Sweden. Just a bit of movie trivia....