1911Tuner/Hammer bounce


May 12, 2004, 02:18 AM
1911Tuner, you wrote that a too light 1911 mainspring can cause hammer "bounce".
Could you kindly explain in detail this effect?

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May 12, 2004, 09:28 AM
I'm not Tooner, but...

I THINK it might be the SEAR SPRING he mentioned? Too light a sear spring (the flat leaf) will not reset the SEAR to catch the hammer when it bounces back from the limit of its travel. Can't figure how the mainspring - the one that works the hammer - would cause hammer bounce.

Maybe that's why I'm not the EXPERT, but an ENTHUSIAST! :D HTH

May 12, 2004, 10:39 AM
Hiwdy MAXM,

Hammer bounce works thus:

When the slide goes to battery at full speed...as with lettin' it slam on
an empty chamber...the sudden stop at the end is what bounces the hammer.

The pistol is jerked forward violently, and the hammer tries to obey Newton's first dictum ht at states: "Objects at rest tend to remain at rest."
The hammer tries to stand still when the pistol jerkes forward, and "floats"
for a split second because a weak mainspring is overcome by the hammer's
at-rest mass. A nanosecond later, the mainspring regains its footing and
slaps the hammer forward, and the sear catches it.

If the left leg of the sear spring is weak or overtweaked, the sear isn't in
the fully reset position to catch the hammer hooks, because it bounces a little too...At that point, the very tips of the hooks are standing on the sear...which makes for about a 8-ounce trigger pull for that shot, or the
hooks miss the sear completely and the hammer follows the slide...usually
to the half-cock.

In extreme circumstances...and everything must be juuust right...the
hammer will catch and jar off the sear just as the slide slams home, and
fires theweapon. In even extremer (is that a word?:p ) The cycle repeats
and the pistol doubles or goes full-auto.

A pistol with a fine-tuned trigger, the sear primary angle is narrowed in order to make the break sharp and clean...and lighten it up a little. The
small angle...often as narrow as .010 inch...is easily damaged by hammer bounce, and after just a few such events, the trigger job will be ruined.

A strong mainspring keeps the hammer in contact with the sear, or at
least won't let it bounce as far out of engagement, so the damage is minimized or avoided altogether. Going strictly by feel, you would be hard-pressed to tell the difference between a 23# mainspring and a 19 pounder.
An accurate trigger- pull gauge might show a difference of 4 ounces, assuming that the hook and sear primary angles are correctly matched,
and that both hooks are bearing evenly on the sear.

Whew! That got a little involved. Hope this clears it up.


May 12, 2004, 10:56 AM
Many thanks to both. Happy to receive so immediate and clear reply :) .

May 12, 2004, 06:00 PM
There is another evil actor that can contribute to "hammer bounce" effect. The trigger also has mass, so it has inertia. When the frame bangs forward after the slide slams home, the trigger tries to remain at rest and therefore applies a tiny rearward pressure to the disconnector/sear at the instant it hits. That "tiny" trigger pull force moves the sear slightly and can add to the separation distance between the hammer hook and the sear nose.... making it worse when the hammer bounces back into contact with the sear. If the sear spring is very light, it can allow the hammer to drop to the half cock notch. This is the reason for those very expensive ultra-light triggers you see on comp guns (and the fact that they look cool).

May 12, 2004, 06:07 PM
And bountyhunter is...Absolutely correct!

Colt Gold Cup pistols have wide triggers, and being wider, they are also heavier. To counter the inertial mass of the trigger doing what bountyhunter describes, there was a tiny preload spring and clip attached between the sear and the trigger that gave the trigger a little help standing still.

I haven't seen one, but it's my understanding that more recent Gold Cups
have aluminum triggers, and the preload spring has been omitted.
(I HATE those things!):cuss:



Jim K
May 13, 2004, 09:51 PM
Hi, Tuner and guys,

That situation of the hammer staying back when the slide goes forward is common and not due to a light mainspring. The slide itself has bounced off the recoil spring guide, and that bounce has returned some of the backward energy that the frame had absorbed. That means the slide is moving quite fast at the first part of its return to battery (much faster than if released manually). The hammer does not follow the slide like the book pictures show, it does an act like Wile E. Coyote suddenly realizing that the cliff isn't under him any more. It hangs for an instant, then falls forward until caught by the sear. (This is shown in high speed photos.) Trigger work needs to take this into consideration or trouble awaits.

The main problem encountered in very light pulls is that mentioned by Bountyhunter. The trigger, in effect, pulls itself due to its own inertia. This causes the hammer to drop into the half cock notch and is why some gunsmiths tell their customers to hold the trigger back when releasing the slide to load the first round. I consider that practice dangerous because it employs the trigger in a role other than firing the gun; training should always be that the trigger drops the hammer, and if the gun is loaded it will fire. Using the trigger to prevent dropping the hammer is, IMHO, counterintuitive and a bad habit (as well as illegal on many ranges).

Some gunsmiths get so uptight about their super sears that they go bonkers if they see anyone releasing a slide without holding the trigger and/or easing the slide down. One "gunsmith" I knew of was so concerned about his "perfect" knife edge sear being damaged by the half cock notch that he ground off the half-cock notch! After some of his customers had magazines empty rather rapidly, he was "persuaded" (by his lawyer) to stop working on guns.


May 14, 2004, 02:22 AM
Hey Jim! Good to see ya jump into one.

Your description is on the money, as usual. My explanation of the event was considered from a release from slidelock instead of beginning with
recoil and slide bounce off the guide rod head.

Yep. That hammer bounces around a lot before it settles down after the gun goes bang. Off the slide...Off the grip safety, and off the slide again
before it drops onto the sear. The inertial trigger nudge is a player too, and is usually the culprit on a followdown, but I've seen pistols do it with the trigger deliberately held forward with a fingertip as well as held rearward before tripping the slide release. Applying a little forward bend to the left leg of the sear spring reduced it, but didn't stop it. Stepping up
from a 17-pound mainspring to a 21-pounder did. Probably a combination.

Still waitin' for a write-up on your Balanced Thrust Vector tests/Recoil...mainly to see the reactions that it gets on the board. Just write up a disclaimer so the kids won't try this at home. That'll be one
hot thread...I guar-on-tee.

Luck to ya neighbor!


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