I've done it, and it's is easy.
1) look under the outer periphery of the pressure gauge and you'll find a hole that is only partially drilled thru.
2) disassemble the gun and remove the parts in the block where the reg will go.
3) There's a black plastic ring in there, and it may be smashed/deformed a bit and hard to remove, but it has to come out. BE CAREFUL not to scratch or damage the inner surface of the hole, because you reg will have oring that seal on this surface.
4) After all is out and cleaned up, take a 2mm drill and finish drilling all the way thru to the inner passage where the reg will reside. Go slow, and oil it often and clean chips out often. When you think you're getting close, go slowly so as to minimize burrs inside. Be careful when you break through not to hit the opposite side of the hole in the block and damage it.
5) There will be a burr in the inside, no matter how careful you are, (at least me), so take a pick, a tiny file or screwdriver and knock down the burr as much as you can. The reg doesn't seal around the hole, it seals ahead and behind it, so all you're looking for is no burr to break loose and cause problems, and being able to slide the inner oring on the reg over the hole.
6) clean everything up and make sure no chips got in the action.
7) check your reg setting is where you want it, and lube the orings well, especially the inner oring
8) slide it in carefully and work the inner oring over the hole slowly and carefully, but don't hesitate to push it in all the way. If by chance you do damage the oring, which isn't likely, you can always remove the reg and replace it. So it's a good idea to have spares on hand.
8) Tuned hammer spring and enjoy
I just sold mine, and i may have made a mistake, but it's time to move to other guns. The Royale might well be the finest rifle FX ever made. There is literally no weak spots in the design. You should be able to reach 30is fpe after the reg install. Mine shot stellar after. I did not change anyting else, and it worked fantastic. I did however tune it, ie hammer spring.
