100% agree with the advice about not stoning down the top surface of the bent to shorten the trigger pull. I have had to repair a number of locks that have had this done, and which invariably end up catching the sear in the half cock notch..
I would also be very wary of reducing the height of the half cock notch as this can result in weakening or taking off the top "hook" surface that is supposed to capture the nose of the sear. The proper way to form the half cock notch is for it to come back over the top of the sear nose and prevent the trigger from being pulled. You should not be able to "go off at half cock" by pulling the trigger. The only way of getting out of half cock should be by going to full cock.
If you do have too deep a full cock bent, then there are a number of ways of dealing with it:
1. Remake the whole tumbler.. this is a bit drastic, but if the original one is too damaged or badly made, this may be the best solution. I would turn the tumbler from round medium to low carbon steel (does EN8 make sense across the pond?) so that the cock square and pivot are in line and then file or linish the profile to a template made from the original. If you take this route, remember to leave a thin bearing surface round the pivots to reduce the friction load. Case harden and polish after ftting.
2. Tig up the original bent and reprofile. Case harden after fitting. This is the normal way I would deal with this problem. By building up the lower surface of the bent, the sear rest point can be raised without changing the release angle of the tumbler.
3. The third way I have seen this problem tackled in shotgun locks is to drill two small holes in the base of the bent and fit steel pins to raise the point of rest of the sear. I think this is a neat and simple way to address the problem if you do not have the time or resources to do anything else. I suggest it is easier and more accurate than trying to solder shims etc. Stoning the heads of a couple of pins makes getting the levels and heights easy, and if you over cook it, just replace the pins. There is almost no load on the side of the sear as it all should be going through the face of the bent so the pins only have to stop the bent in the proper place. From what I have seen, this seems to have been a standard 19th C solution to the issue in the UK.
Regarding trigger pull, another source of friction is the tip of the trigger bar fouling the wood of the stock at the base of the inlet. This can be caused by poor inletting or by wood shrinkage allowing the lock to set in further against the strain of the lock pins. A blob of blue on the end of the trigger bar should show if it is fouling. I find an end mill held in a hand drill is useful for deepening lock inlets without mashing up the wood. You need to use a sharp, preferably new three or four blade mill as you only want to skim the surface. Be careful if you use a slot drill as it tends to dig in and cut too much. You can do this with everything mounted in a milling machine, but I would not run it under power.. just turn the spindle by hand...
