The function of a 1911...or any autopistol...depends on everything happening at the right time. Timing is controlled and determined by the inertial mass/weight of a given part or sub-assembly, and the spring that drives it. Every solid object weighs something. That weight determines how much resistance that object resists movement or a change in direction.
The spring that resists and propels an object also has weight, but its function is determined by its rate of resistance. Recoil springs are rated in compression, but an often overlooked factor is the rate that it unloads its stored energy and returns to its relaxed state...or as far as it can go before being forced to stop. The stronger the spring, the faster it unloads this stored energy, and vice-versa. Timing!
Fast-forward to hammer/sear interface, and morph yourself down to about a millimeter tall, so you can watch the event in slow motion.
Browning's original design for this interface provided slightly undersquare hammer hooks of about 1/32nd inch long, and a matching...or agreeing angle on the sear. This provided a captive engagement that tended to force the two parts together more positively. Browning did this because he understood inertia and how easily that those surfaces could disengage under its effect. This captive engagement provided a margin for error that made the gun less likely to burst-fire, but didn't do much for the trigger pull because as the trigger is pulled, it actually pushes the hammer farther back against mainspring tension. Triggers in ordnance-spec pistols generally ran from 6 to 8 pounds, depending on other factors. Safe, but not conducive to precision shooting....which wasn't the intent anyway.
When the slide recoils and cocks the hammer, the event is fairly violent. The hammer overcocks, bounces off the grip safety tang, and the mainspring forces it back down. The face of the hammer hits the slide, and bounces again before it settles down. The slide returns to battery, and the hammer falls further, and is stopped by the sear primary angle catching the hooks.
The slide goes fully to battery, and depending on how smoothly it chambers the round, jerks the pistol forward and slightly down. The hammer, being on a pivot via the pin, obeys Newton's law, tries to stand still, and breaks the contact with the hooks to some degree. If the mainspring is weak, it breaks contact more easily.
Enter the trigger. The trigger has mass and weight. When the slide slams to battery, the trigger also obeys Professor Newton, and stands still as the gun moves forward. During the firing cycle, the effect is eliminated because the trigger is held rearward at the limit of its travel, and is disconnected from the sear...so it doesn't have any EFFECT on the sear.
When the gun is being loaded or reloaded with the finger off the trigger, this all changes. The trigger is connected to the sear via the disconnect, and is free to move. Actually, the gun is moving and the trigger is standing still. As the gun moves forward, the trigger stirrup nudges the disconnect, and tries to rotate the sear out of hammer hook engagement. If the hammer's contact with the sear is already lessened through a light mainspring, the sear can escape, and the hammer will fall.
If the sear spring is up to the task, the sear will go back to engagement position, and grab the half-cock notch, stopping the hammer. If the spring is weak, or has been "tuned" to lighten the trigger pull...it might not stop the hammer, and a slam-fire can result...but usually all that happens is that the hammer follows the slide, and comes to rest on the slide without firing...A complete followdown.
The sear can also partially engage the half-cock...or grab it right on the edge, which can damage the sear's primary angle. There is also the chance that the sear will engage the hammer hooks right at the edge. This is known as a false engagement, and will allow the gun to fire with a light nudge on the trigger. Here, the pistol is right on the verge of a burst-fire event.
Enter the "Trigger Job". Military armorers soon discovered that the engagement angles between the sear and hammer hooks could be changed to make for a better trigger. The hooks were cut square, and the primary angle on the sear altered to agree with that square angle, and thus began the match-grade trigger. Cutting those long hooks shorter and shorter produce better and better triggers, but they found that, beyond a certain point, they became too short for safe and reliable function, and they started playing with sear springs and varying mainspring loads and rates and cut a secondary, or breakaway angle on the side opposite the primary angle.
OOPS! The trigger's mass was the fly in the ointment. It would still nudge the sear out of engagement...so they had to keep the trigger pulled to prevent damage to the narrowed primary angle and crown They lightened the trigger. They lightened the sear. They lightened the hammer. They had to change things in order to compensate for the improved trigger in order to make it function correctly.
Fast-Forward to the 80s...People began to demand better triggers on their 1911s, and were willing to pay for it. Manufacturers responded by giving the public what it wanted, and began to square up the hammer hooks, although they left them long enough to provide a margin of safety, and triggers were better...but still not quite match grade. They were lighter, but didn't break like the proverbial glass rod...and that's what people wanted, for some obscure reason.
About this time, the aftermarket parts suppliers jumped in up to their necks, and provided lighter mainsprings...altered sear springs...hammers with pre-cut hooks that were a little too short for comfort. They also included a disclaimer. "These parts should be installed by a qualified gunsmith." All these modified parts provided for some very nice, crisp triggers, but they also created a lot of dangerous guns when the disclaimer was ignored and the parts dropped in by the gun owner who didn't understand the "Engineer's First law"...to wit: "Whenever one thing is changed, three other things must be changed to compensate for the improvement."
Bottom line...The trigger group...or fire control group in the pistol is a system that was carefully worked out and proven. There is a window of operation that allows for wear and light damage. The farther from original design parameters that we stray, the narrower that window gets. No such thing as a free lunch, I'm afraid.
The critical parts in the fire control group are:
Mainspring, hammer strut, hammer, trigger, sear, sear spring, disconnect, firing pin and spring. Each one of these parts has an effect on the others to some degree.
Randomly changing any one part of that system without bringing the others into harmony with the change is risky. You may get away with it and you may not. You may THINK that you've gotten away with it until a little wear occurs, or a spring loses some of its original tension...and things can get informal rather abruptly. Ignoring the gunsmith's dictum that "There's no such thing as a Drop-In part" can bring you to grief.
John Browning had very good reasons for his specified spring rates and dimensions. I'd be willing to bet that if he were to fire a 1911 with one of the current 3-pound triggers, he'd probably be shocked and would advise the owner to get it fixed before somebody got hurt.
Stand by for Part 2.