Gundogblue---You can (maybe) if your bullet length and the final COAL isn't excessive. I have the same set of RCBS Cowboy dies you mentioned, loaded many many rounds of Colt 44 and 44 Special rounds. Bought to reload for Uberti conversion Richards II and Open Top revolvers chambered in 44 Spec. Always loaded black power in the Colt 44's and smokeless in 44 Spec brass, using 200 grain soft lead bullets. When I wanted to expand the 44 Special loadings to higher pressure/fps, not being able to shoot them in the Uberti replica's, I bought a Ruger Super Blackhawk (44 Mag chambering). I found I could reload some jacketed bullets for 44 Mag and smaller grain weight hard cast lead bullets, but the bullet seating stem and the seating/crimping die had to be turned up to to the max and that was iffy depending on bullet length. I always seat a bullet and crimp in separate stages 99% of the time. The longer 'Keith' style cast and other SWC bullets were impossible to seat, so I purchased a separate 44 Mag bullet seater/ crimp die form Midway and that solved the problem.
The RCBS Cowboy dies are really nothing more than standard carbide 44 Spec/44 Mag dies that have a slightly larger diameter case mouth belling stem in that die and the dies are coated with a gold finish, I assume the bullet seating/crimping die must be a bit shorter also. I've never measured the differences between them, but will have to just out of curiosity. Anyone with the standard dies can load anything from 44 Russ up to 44 Mag with no problem, you just have to turn dies and stems up and down to meet your needs. If a shooter wants to reload 44 Russ/44 Colt/44 Spec for the Uberti style revolvers they don't need to buy the RCBS Cowboy dies specifically to do so. Just turn the case mouth belling stem down a bit more. You can even purchase the stems used in the Cowboy dies from outfits like Midway or direct from RCBS. IMO the Cowboy dies were offered by RCBS to catch Cowboy Action Shooters and those wanting to reload for the conversion style revolvers. Sort of like the old saying that fishing lure makers make them to catch fishermen, not fish! In their product info, RCBS states that the Cowboy dies were made to accommodate the use of lead bullets, so lead shaving wouldn't occur. That can be accomplished with the standard set by just turning the mouth belling stem down a bit more than used for jacketed bullets, but not to excess where you split the case. Just my experience with the Cowboy dies. I reload 38 Special ammo using black and SL powders for a Uberti Richards/Mason replica revolver using my standard 38/357 Redding dies with no problem. The Cowboy dies are a good set, will do what they are suppose to do, just aren't geared for the full array of bullets used for 44 Mag reloading.