You can do a trigger job on any firearm--but you have to be aware of some basic (but very important) guidelines.
1. The actual contact surfaces between sear notch (hammers) and sear noses (triggers) are hardened. The contact angles are set. If you stone these angles to the point where you have changed the engagement angle in any way, you have broken through the heat treatment--meaning that there is a limited lifespan left to those parts before they become unserviceable.
2. Most action jobs consist of eliminating binding points on the moving parts that compose the ignition system. Some problem areas are:
a. The sides of the hammer v. the frame
b. The sides of the trigger v. the frame
c. The bearing surface of the hammer and trigger pins v. the bearing surface of the hammer or trigger.
d. The sides of the sear v. the frame.
e. The movement areas of the recoil and main springs.
f. The trigger return spring itself--which is USUALLY the thing governing pull weight--NOT the sear angles.
To smooth out a trigger pull, first make sure that any rough spots, burrs, shavings, etc. are removed from all contact surfaces. I have found that a medium and/or fine India stone works well here. Use a good clean oil to lubricate the stone for a smooth cut. Make all of your stoning passes exactly square to the work surface; use a light and even pressure. Don't overstone either--go slow and test fit often.
You might have to go as far as a light application with a file for some serious burrs or nicks. I recommend the use of a good Swiss pattern file. Here, clean your work before you start, and use a good cutting fluid or oil. After filing, clean up the work with some light passes with the India stone, followed by a ceramic or hard Arkansas stone.
Go ahead, and inspect the sear engagement surfaces. If it is chipped or uneven, your best bet is to try to get another set. If you can't do that, then stone VERY lightly with a hard ceramic or Arkansas stone. Use lots of oil, and go VERY lightly.
Finally, use good lubrication for the pistol or revolver's action. You would be surprised at what a good cleaning and proper lubrication will do.
In closing, remember the basic rules of gunsmithing:
Drop in parts usually aren't.
Always go slow, with a lot of fit and try. You can always take more off, but you can't put it back on.
When at all possible, think twice before trying to "loosen" up a tight gun. Try lubing the parts first with some good, thick motor oil, then hand cycle about 50 to 100 times. The metal involved will usually burnish itself.
When in doubt, DON'T.
Have plenty of good written references nearby.
Brownell's is an excellent resource; give them a call and talk to their tech services department--which is, of course, gunsmiths.
And the single most important rule is:
ALWAYS cut on the cheapest part first.