It is perfectly acceptable and safe to use data for a different but similar bullet. Use a manual from a different manufacture, find their 200 gr RN (you didn't specify if it was lead or jacketed - it does make a differance) and start at the that manuals minimum load and work yourself up.
Be aware of any pressure signs as you work up.
Seat the bullet to its cannuler, or to where it will fit the chamber of your pistol.
ETA: If the Rainier bullet is a plated bullet, use data for a a lead RN bullet.