Just came across this post and although late I thought I would put in my penny worth.
Generally I would agree that trigger pulls are best left to the pro but having taught myself with only the help of a sketch on a scrap of paper by a friendly gunsmith, I feel it my duty to pass on my modest experience.
Trigger pulls SHOULD BE the interaction between the angle on the sear nose, the angle on the bent and the power supplied by the main spring.
Yes, there is the issue of binding components, bodged bents, softened (or never hardened) sears but lets assume that the lock is sound, well designed and not messed with.
In essence, when you lift the sear out of the bent, it raises the tumbler ever so slightly against the main spring. Working against the main spring and sear spring and friction between the two components gives you the weight of the trigger pull.
Assuming that the sear and bent aren't corroded or gummed up, we can ignore friction as it should be reasonably constant (by the way, don't try polishing the sear or bent or your pulls may evaporate instantly!).
Firstly, clean all the components and reassemble and re-test. If there is no improvement....
So what you are trying to do is to adjust the pull weight by changing the angle of the sear nose ever so slightly to increase or decrease the amount of extra load it puts on the main spring as it moves out of the bent.
An example to explain the process is the way a door catch cams itself into the latch.
Remember, the amount you are adjusting the angle by is very slight. I use lots of magnification and a 80mm fine (read worn-out!) diamond flat file. I smoke the sear so I can see exactly how I am touching the nose and only proceed a little at a time. I always cut in the same direction as the sear will move to avoid any increase in friction.
I then rebuild the lock and gun, work the lock at least 10 times before taking a series of readings until it stabilises and then average the last 5.
With very heavy locks, I find this is often caused by the sear nose being almost a knife edge yet the bent is of normal depth. This means that the sear if having to climb Mount Everest to get out plus there is often a catch on the edge of the bent which makes the pull so heavy. In this case one needs to reduce the depth of the bent before any meaningful adjustment of pull can be undertaken. Adjusting these knife edge sears can be fun!
If you still want to have a go, don't practise on your pride and joy, find a few clunkers and mess with them first.
