The guns used in all of those movies were probably owned and provided by Stembridge gun rentals in CA....At one time, their arsenal was as big as a small country. I think the US Government borrowed some firearms from them once.
They are now owned by ISS or "Independent Studio Services". They seem to keep good records and I would imagine they know where that particular gun, (or multiples of it used in filming), is located.
No doubt they were but IIRC one of the guns used in MF ended up being presented to John Millius - it could have been the one in the NRA Museum but that is too long ago to remember.
John Milius bought acreage around Gunsite long ago and he was acquainted with the Coopers but in all my trips I never ran into him - I think he actually lived somewhere else. John suffered a stroke but the last I heard he has recovered enough to shoot a little.
John is an interesting guy but I don't wan't to wander off down that bunny trail in a thread on J Edgar Hoover's .357

Riposte