The sear-hammer engagement on a 1911 are so tiny it is hard to picture them. It's, what? 1/16th of an inch in contact area?
On the full cock notch on the hammer, those hammer hooks have to be the same height. People can intuitively understand that it is not good for the sear to drop off one hook and then the other.
And that is the easy part.
There is a facet on the sear that contacts these hammer hooks. Or it should be a facet. If you look close on lots of factory guns this part actually looks rounded. You have to make the facet angles on the sear a certain way so it contacts the hammer hooks a certain way to A) get best results, or, failing that, B) NOT BE UNSAFE.
Neutral: Full contact. Spring tension holds this in place. Ideal.
Positive: Harder to trip but when you let off the tigger the sear wants to return to fully engage the hammer, all the way into the notch. Not the best trigger feel, and that edge will wear down over time to more of a rounded face. I think factory triggers end up erring on the side of a Positive Sear Engagement because it is safer.
Negative: Unsafe. That angle the sear want to creep out of the notch and the only thing holding it there once it starts to creep with the barest trigger pull is spring tension. The slightest vibration and it can trip, causing a Bad Event. You can go a long time without this bad event happening, but, it's only a matter of time.
In those diagrams I show the facet angle but in contact, when the pistol is cocked, they look more like:
With negative engagement the gun doen't want to return to the above diagram when you stop applying pressure to the trigger. It wants to creep out from under.
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When you take your 1911 to the gunsmith for a trigger job this is what he is doing. Probably fitting a new hammer unless the original one has plenty of meat on it (this is often the case) to adjust the hammer hook height and faces, but almost always getting a new, good, sear and putting the correct angle on it., If your gunsmith knows what he is doing. And doing this right is NOT EASY. Because of the tolerances and differences between guns this can't be a drop in part. Two frames made one right after the other may have slightly different angles to the pin holes alone that hold the hammer and sear in the gun.
If you have a good neutral sear engagement with lots of good contact you can see after using a smoke lamp on that facet, THEN you can play with the leaf spring fingers to get a crisp trigger or a roll trigger, 5 pounds or 3 pounds.
All THIS is what modern plastic pistols seek to improve upon. Make these critical angles unimportant, or less important, and the parts truly interchangeable without a high degree of skill and ability with the assembler. Things like this are why 1911s are expensive and striker fired tupperware are not. Cheaper materials, cheaper parts, less critical angles result in a well functioning plastic gun that is cheaper and easier to maintain. And that is ok.
"But I love 1911s, and don't want mine to be a dog or unsafe, T-Bolt! What do I do? I spent a grand on this and it might be unusable?!! WTF?"
Relax. The hard part for you is finding a good gunsmith to do a good trigger job. A true neutral sear hammer engagement. Your frame can be rattly and finish look horrible and the headspace be loose, but if you get that $200 trigger job (or less) on your gun and you are almost to aces. Something you love will bring you more joy.
After that their are other easy improvements. Change out the recoil spring and firing pin spring. Adjust the extractor tension. Or replace and adjust the extractor tension.
"But I love 1911s and want to compete at a high level in Bulls Eyes competitions, T-Bolt, where inch groups at 50 yards is critical!"
Jeez, you want egg in your beer, too? To get that requires a bit more work. You aren't getting out of here only spending $1000 on the gun and $300 worth of gunsmith improvements.
"It's OK, T-Bolt, I just popper for a $3500 custom Wilson 1911..."
Hssss... yeah... you might be alright. You might not.
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