I have 'em, I guess I could go freeze frame it and zoom in and see if I can read the stamping. That would solve it once and for all. I know everyone is dying to know. In the very beginning, he tells the would be robber the famous line, "This is a .44 magnum..."
FWIW, in the second one (I think the second --the one with the renegade motorcycle cops) he is shooting at an indoor range, he walks in on those guys. They have a discussion and shoot some targets and one asks "what loads do you use" and he basically responds "I use specials, in this larger frame it improves control".
Those are not the exact quotes by the way, but that is what was said.
Later in the first movie he also deploys a .458WinMag as a sniper rifle, and in the later sequels moves to a (Wildey?) semi auto.
Funny thing is I carry a 10mm for almost the same reason he carried the .44 loaded with specials... I also carry a .40 sometimes, but perfer the 10mm. A large frame handgun with reduced loads loses little in performance but gains a LOT in controllability. My buddy's 16yo daughter, she hates the recoil from my G27. But she loves the G29 when loaded warm... My wife, who is VERY recoil sensitive, she feels the same way.
Everyone loves shooting specials through my 686+. Not nearly as many like shooting 125gr. XTP's at 1700+ fps though. I think if I were to carry a .44, I'd probably load it with specials or some kind of soft custom mag loads. Better performance than a .45ACP, much more control.