Dear Sirs, Can I use a set of .500 - 3 1/4" RCBS dies to reload .500 - 3" Will I have no trouble doing the crimp? Thanks in advence, Hector

As in the .500 Nitro Express, .50-120, etc, as long as the cartridge walls are straight, there will be no problem.
Back off you dies the distance needed to resize the neck/mouth area.
The crimp die should be backed off, the cartridge placed into the press, and the handle lowered.
Slowly screw in the seating/crimp die until it touches the case mouth. The screw in the die 1/4 turn at a time until you get a crimp you want.
Be careful not to apply too much crimp as the case can buckle and be ruined.
The only problems I have ever encountered is that the seating dies "stem" would be too short to properly seat the bullet to the proper depth.
I had to by an extra long seating stem from RCBS.
If you are never going to load 3 1/4" cartridges, you can have a friend with a lathe turn off the bottom of the doe set to 3".
I have done that in the past as well.

Thank you Sir.