It appears I've been able to solve the hammer follow problem.
Sully, you were on track with regard to the disconnector. The issue was manifold, and all the fire control group parts were involved to some degree.
Here is what I did (summary):
- Replaced, Trigger, Hammer, Sear, Disconnector with new parts from Wilson's Bullet Proof line of components.
- Replaced Sear Spring (Triple leaf spring) with a Clark "Custom Sear Spring" (the disconnector leaf is bifurcated on the Clark spring).
- I had to fit the existing thumb safety to the new sear, this was done slowly and iteratively with a file and several test fits and function tests (what a putzy pain in the ass, but I did not want to get this step wrong and create a dangerous malfunctioning thumb safety sear block).
- I had to fit the new disconnector by filing off the shoulders of the plunger portion of the disconnector to make sure the disconnector engaged the slide recess properly, otherwise the shoulders were too wide and the disconnector acted like the slide was out of battery, blocking trigger pull, (I was able to use the previous disconnector as a model for how much material to remove and get this step done in one try).
Here is the current state:
- All function tests pass, (including the hammer follow test), but I have not test fired the pistol yet. I may do that today, if I complete all chores and family duties first.
What I think was wrong:
Several things appeared to be interacting, but each alone seemed to prevent proper function and allow hammer follow.
- The sear spring did not engage the sear or the disconnector properly, the previous owner or his gunsmith stoned the disconnector leaf top to smooth engagement. It looks like they stoned too much off, rather than just adjusting the angle of the engagement. This in turn shortened the center leaf spring enough to allow the pistol to not always disconnect properly and explains some of the frequent hammer follow and occasional double fire.
- The sear shelf on the trigger was slightly shorter than 0.020" and not perpendicular to the trigger (past 90-degrees) allowing the sear to slip off the shelf. In addition, the hook of the half-cock shelf was completely ground off, and the remaining shelf appeared to be too shallow.
- The engagement surface on the sear was well honed, but it appears too much was taken off and the sear is ever so slightly too short to properly engage the hammer sear shelf (so the trigger was already following the slide for that ever so small 0.00x" or so, and the hammer momentum along with the improper sear shelf height and angle allowed the hammer to slip past the sear rather than engage it). I did not measure the distance from the sear's pin hole to the sear engagement surface, so I admit that I'm speculating on this one.
To be able to do this myself, I ordered several books to study up on the 1911, but the biggest help was YouTube videos and many cycles of disassemble/fit/reassemble/test to understand the part functions and interactions.