Yep. Did it once; no ill effects.
Range session with the EMF/Uberti 7-1/2" .45LC. Ammo was in one of those 50-round zip-lock loose bulk bags picked up at the gun show--nickel brass, lead round nose, except for one with a jacketed soft point. No biggie, just one of five rounds chambered in the Uberti. During the five-shot string, one of the rounds went off with considerably more vigor than the others: louder report, more flash, but no noticeable increase in recoil.
'Wow, that one was sure different.' When the empties fell out--and they all did easily, with no prompting from the ejector--a quick study of the case heads showed that one was a .44 Mag. It had been in the bag all along, unknown and unsuspected--49 .45s and one .44. No split case, no bulged case, no abnormal signs of any kind on either the case or the gun. Probably, as has already been mentioned, the smaller diameter bullet went down the larger barrel without having a chance to build up any excessive pressure.
The moral of the story: No more gun show plastic bag bulk ammo. Period. And no ammo except factory or my own handloads. That was a once-only experience, and I intend to keep it that way.