Tuning locks requires a very experienced sidelock specialist, with a very small file John. I was fortunate to have Dan Lammers tune mine and the trigger is now a thing of wonder, which has spoiled me and worsened my hopeless flinch with a heavy, creepy trigger
The other issue is that after thousands of shots, the upper edge of the tip of the sear (usually the right) becomes rounded, causing a light trigger pull or doubling.
Courtesy of David Williamson
If you'll tell us where you are, we might be able to recommend someone nearby.