I'm not in the movie business or anything, but to me it appears that the twin revolvers used in 'Van Helsing' had much more than a bit of 1878 Mauser Zig-zag Revolver ancestry.
There certainly could be modern revolvers hiding inside there, but there also were a lot of knock-offs of the Mauser revolver made, notably in Belgium, in the later part of the 19th Century. Original German ones were desirable but expensive and the Belgian (and Spanish) gun industries were more than willing to create knock-offs, some of them quite elaborate.
There are good photos of original Mauser Mausers on the Belgian website littlegun.be: compact revolvers, full-sized and even a carbine, and the basic Mauser pistol design in 2 different models. They even have an excellent photo of an original gun completely stripped down.
I really think that this is at least the genesis of the strange revolvers used in the film.
