The DA New Service, usually with ejector rod braised onto the barrel, is used to "duplicate/replicate" the 1878 DA Frontier which was produced in .45 and .44.
The Frontier and the so-nicknamed DA Thunderers and Lightnings were very common Colts in the 1880s and onward.
For movie purposes, I believe it's hard to come by working models of the Frontier as most are really very much collector items and weren't produced into the 20th century as were the
SAAs.
Interestingly enough, the 1878 models had the cross pin spring loaded retainer for the cylinder pin while the SAA didn't get that design until the mid 1890s. Because of Army contracts, Colt didn't want to introduce the cross pin which would have complicated Army armorer maintenance of the SAA. The screw through the front of frame worked pretty well but wasn't ideal.
Where the "1878" becomes so noticeable as a fake in movies is when the actor must reload and swings out the cylinder to the left.
The New Service also was used a lot when the studio needed an actor to fire fast multiple shots. I've seen it where the hero carries a SAA but shoots a "Frontier" during the fast draw/gunfight.
Actually, Hollywood is trying to be "accurate" even though nearly all Western movies have nothing to do with the real old West.
It's the Buscadero holster where Hollywood goes far astray for films placed before the 20th century. Alas, Matt Dillon's leather rig wasn't factually correct.