One method for inletting detailed trigger guards is to use a very small "chisel" made from one of those tiny screw drivers used for eye glasses. By small, I mean maybe 1/8" wide, smaller is even better. You can put a nice edge on them by carefully grinding. I've found that their usually tempered well enough that you can get away without any further heat treating. Firmly clamp the trigger guard in place and stamp all around with the small chisel. Remember to put a slight draft on the trigger guard, and it should be very tight without gaps.
I hesitate to say this, but another method that also works very well is to heat the trigger guard, then set it on the wood where it'll be going. You don't need to get the brass red hot, just hot enough that it leaves a mark. It'll leave a perfect outline for you to go back over to stamp and inlet. You're NOT burning the trigger guard into the wood. A little practice might be needed, but it's an excellent method for "fancy" trigger guards...
Ed