PP,
Are you talking materials, or dimensions/design?
If materials, I can't give you steel types or exact heat treatments.
I spent an interesting half hour on the phone about 8 years ago when Bob Munden called one day. He went over some aspects of how Colt makes the Peacemaker, and even though it's not still made the exact same way as it was 100 years ago, some things remain very similar.
Colt has always been careful to use (after the initial iron frames) high-grade ordnance steels in that gun, with attention to proper heat treating as that branch of the gunmakers' science evolved. Frames are still forged. Action parts are not cast. The Colt still uses a firing pin bushing, and that was a whole story in itself. Munden said there was one man at Colt who did the case hardening on the frames, and it was done the old-fashioned way, not chemically applied. And so on. For exact materials specs, you'd need to contact Colt.
One traditional & long-running problem with the Italian clones for decades was that the Italians did not take those guns seriously. Originally, when the Peacemaker replica industry started up, nobody was shooting them anywhere near as much as the CAS people do now. Uberti built functional replicas, with lesser (compared to the Colts) materials, and took design shortcuts such as eliminating the firing pin bushing, not fitting a removable/rotating cylinder pin bushing, changing dimensions, using cast parts, brass gripframes, and not properly heat treating internals. Those guns worked OK for a while when used sporadically, but the guts were soft, not fitted particularly well, and tended to wear much sooner than a properly fitted Colt SAA. I have personally run across one replica with a trigger tip (sear) so soft it actually rolled with use, leaving a VERY light trigger pull (not surprising, since there was almost no engagement with the hammer notch left). Other problems I've seen are bad springs that break (main & hand) with relatively limited use, bad headspacing, bad timing, firing pin breakage due to a misalignment with the firing pin hole in the frame, etc. This is not confined to Uberti.
One of the big selling points for the original American Western Arms was the fact that they claimed to be shipping genuine US 4140 ordnance steel to the Armi San Marco factory in Italy to use in building the AWA clones.
Cimarron Arms tells me Uberti has been using 4140 for a while now. But, they apparently weren't always.
With the CAS engine powering the clone market, importers have put increasing pressure on the Italians (ya should oughta hear some of the horror stories these guys can tell about dealing with them) to improve overall quality, and in most cases the QC has improved markedly in the past 10 years, especially with the new Uberti plant. They are finally taking the guns more seriously, and building them to last longer in actual use. In most cases, tolerances have tightened up, parts are getting better heat treating, and materials themselves may be getting upgraded in some areas.
Again, for the exact materials specs on the Berettas, you'd need to contact Beretta.
And, you could be right on the USFA thing. Some of the rumors that are still floating around can be surprising.
Denis