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Discussion Starter · #1 ·
I’ve spent some time looking at sear and hammer geometries and much to my surprise have concluded statements made about trigger “feel” and trigger pull weight are not due to the type of sear and hammer engagement. Maybe this view has been raised in this forum but after searching I haven’t found it. Instead I have found the opposite much discussed. I recognize my observation may break long held thinking.

Assuming reasonably accurate hand finishing of sear and hooks, the differences in trigger pull and the “feel” assigned to the various types of engagements (positive, negative, or radiused) is below the level of human perception. It’s my current view that reports of one type of engagement being better or feeling better then another likely exists in one’s mind.

To demonstrate try this simple experiment. Dry fire your pistol with the three finger leaf spring removed. You will likely discover a sear which is clean and lubricated has a trigger pull of about 3/4 lb. One can barely sense 3/4 lb on one’s finger, let alone assign a poor feel to it. To gain a sense of what your engagement alone truly feels like you will need to point the barrel straight down when pulling the trigger so the disconnector slides unaided into place. This result leads me to conclude the presence of a poor feel lies somewhere else.

I then performed a different experiment. I reinserted the leaf spring and lifted the hammer strut so the mainspring would not be compressed when cocking the hammer. At full cock, I measured the trigger pull to the point where I first saw the hammer drop (pistol was held upside down in a vice). The pistol showed about 2.6 lbs. This confirmed trigger pull is significantly driven by the leaf spring. Maybe poor feel lies somewhere in the chain which creates 2.6 lbs. [My trigger pull is 3.25 lbs with mainspring in place, the mainspring is 19#]

These results were not what I have been lead to believe. So I built a solids model of the 1911 trigger system using Solidworks. From the model I’m able to fully see how all the parts interact, rotate about their centers, and slide against each other. The level of precision of the model far exceeds the manufacturing precision of the parts themselves. I can, in effect, bring to bear a 1000x microscope with measurement tools that can accurately resolve to far better the 0.000001” and 0.0001 degs. The individual parts were built using the nominal dimensions of a 1911A1. I didn’t perform a tolerance stack-up to account for the allowed dimensional variance from nominal.

Using the dimensions of today’s hammers, a sear with a flat engagement surface at 90 degs will have negative engagement with the hammer hooks [Note: Modern hammers differs from the drawings]. That is, only the outer corner of the hammer hooks contact the sear engagement flat. When the hooks are also cut at 90 degs, the inner face of the hooks (typically 0.020” high) never touch the sear at initial engagement or during sear rotation. The use of dykem will confirm this.

For a 90/90 deg geometry the angle formed between sear flat and hook inner face is 2.3 deg. Hence the likely reason many see them as parallel and mistakenly label this a “neutral” engagement. This means if one cuts the hooks to greater then 92.3 deg or the sear’s flat less then 87.7 deg one will have positive engagement. Creating a 90 deg hook is easily achieved with a good square stone. Creating a 90 deg sear flat is also rather easy with proper use of something as simple as an Ed Brown Sear Jig.

The 2.3 deg angle between sear flat and hook face means the hammer falls with sear rotation. The drop is about 0.0006”. Just for the moment, assume the hooks drop a much larger 0.002”. Does this cause a detectable change in trigger pull or feel?

Using the solids model, 0.002” of hook movement causes a change in mainspring force of about 0.02 lbs (a 23# mainspring has a spring constant of about 30 lb/in and a much shorter moment arm then the hooks). Mapping this change in mainspring force to the change in force at the back of the trigger bow shows the change in trigger pull to be about 0.0005 lbs. I don’t think a finger exists which is sensitive enough to feel this.

When manufactured according to print, a sear has an engagement flat which is 90 deg to a line extending from sear pin center to the sear tip [Note: the sear tip is now defined as the bottom edge of the 45 deg chamfer]. How close to 90 deg does one need to cut the sear flat to be at (or under) 0.002” of hammer hook drop?

Solids modeling shows one can be off by 5 deg from 90 and have just under 0.002” of hook drop. For an attentive 1911 owner, miss-cutting the sear by 5 deg is unlikely. The Ed Brown Jig, with thoughtful use, will hold one to within 0.5 deg.

It is often said replacing the standard 23# mainspring with one of lower force reduces trigger pull. After exchanging my 19# spring with a 23# spring I remeasured trigger pull with the leaf spring absent. The 23# spring showed just about the same 3/4 lb.

Considering this evidence, I have difficulty seeing one can objectively detect a difference in trigger weight or feel for negative, positive, or radiused engagement assuming one holds reasonably close to a 90/90 geometry.

[Pistol details: S&W Pro Series 1911. The sear’s engagement flat is 0.017”. The 45 deg chamfer is 0.009” wide. The hooks are 0.022” deep. The latter two numbers imply 0.013” of the sear flat are under the hooks.]
 

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Experienced bullseye shooters can and do sense the qualitative differences in various sear/hammer treatments. That is not me nor obviously you.
Those sensitive shooters can detect other minute differences in the trigger group. Spring preloads etc.
Joe
 

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I agree with much of what you are saying. A big problem as I see it, is so many mistakingly make judgement calls on various triggers. I’ve spoken of this for years. Triggers are the FIRST bit of Gunsmithing I learned, back in ‘99. I’ve set up, modified, improved every trigger on EVERY firearm I’ve ever owned! I’ve put the time into what I do. And know every aspect of function in great detail. Forever it’s been the case, a kid puts a lighter spring in his gun & does the infamous “$.25 cent trigger job” polishing....and all of a sudden they are EXPERTS in setting up triggers! (Oh, BTW, a little info guys. A Dremel is NOT a triggers friend!) You are correct about how people perceive things. I’ve proven before that a 4lb trigger can FEEL better than a 2.5lb trigger in certain circumstances. With the 1911, the trigger bar channel can add to trigger feel as much as anything else. Creep & Over travel are also elements that can stick out like a sore thumb. Both come into play with the term “breaks like Glass”, where you want the trigger shoe to give you that feeling of falling away from your finger. I always explain it like breaking an ice cycle on a steel railing. Most of us know exactly that feeling when we think of it. We can visualize the weight being there, then just gone!

Now, many of us here & on other firearms forums have spent a great deal of time in research & in practice of trigger work. But for every one of us, there are 20 or more kids who just stuck some trigger parts in a gun, and are then on the Gunsmithing forum giving everyone a play by play of WHAT to do for a LIGHT trigger pull! Or even better...they start using terms like “competition” vs “tactical” triggers! Yeah....that’s what I want...one of them “Tacti-COOL” triggers in my gun! Gimme a break!
 

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Discussion Starter · #5 ·
Experienced bullseye shooters can and do sense the qualitative differences in various sear/hammer treatments. That is not me nor obviously you.
Those sensitive shooters can detect other minute differences in the trigger group. Spring preloads etc.
Joe
I tend to agree. However, all I shoot is bullseye. Which is why I finally decided to spend the time to study the 1911 trigger system in depth. I was looking to understand what the big drivers are and how they may affect feel and trigger weight. One of my conclusions is the manner of sear/hook engagement is not one of the big drivers.
 

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Well done post. I would disagree with your major point..not being able to feel the difference in pull created by the negative, positive and neutral relationships. There are excellent world class shooters who are very particular in the feel and nature of the trigger pull. I can feel it.

You are correct, the mainspring typically will contribute only a fraction of the total pull force. Put a positive relationship between the sear primary and hooks and the pull force contributed by the mainspring increases. Been there, done that. Get into the really heavy mainsprings, the difference can be can be greater.

Again, well presented post.
 

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Discussion Starter · #9 ·
I would disagree with your major point..not being able to feel the difference in pull created by the negative, positive and neutral relationships. There are excellent world class shooters who are very particular in the feel and nature of the trigger pull. I can feel it.
I agree world class shooters can feel a difference. But what is the source of that difference? That is the question I'm trying to solve. My thought is it isn't in the sear/hooks geometry.

I'm going to be simplistic for the moment so we don't yet get lost in the weeds. If a 3.25# trigger at break is composed of 0.75# due to the mainspring acting on the sear/hook the remaining 2.50# stems from the left and middle fingers of the leaf spring. Let's say world class shooters can sense a rather tiny 0.2# (or 6%) variation. This variation is only important after take-up and just till break. Anything after break should be ignored just as the best shooters train themselves to ignore recoil.

A 0.2# variation in 0.75# is measurable (it's over 25%). Yet my solids modeling shows a reasonably well cut sear and hook will have a variation about 1/400th of that. A simple change in the coefficient of friction between sear and hook could be the source. But all forms of sear/hook geometry are equally effected. The distinguishing difference of the geometries is the amount of hook movement. Yet the movement is too small to generate a meaningful change in the mainspring force.
 

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Discussion Starter · #10 ·
I disagree with the statement as well. The best triggers are the result of perfecting the designed engagement.

LOG
Okay. But what design features move one in the direction of perfection?

My current thinking is engagement is not the main driver. The interaction between left and middle fingers of the leaf spring, disconnector, sear, and trigger bow provide the vast majority of trigger feel and weight. Maybe that is where one should focus.
 

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Undoubtedly the sear spring has always been responsible for the final pull weight, past what's needed for a dependable safe trigger no matter the final pull weight. Trigger bounce hammer follow and doubles are not tolerable and the result of changing the geometry from the original design of the sear primary being the 90 degree from the line passing through the pivot to the tip, and the hammer hook tip landing tip first on the primary having a polished radius on the tips. Changing the hook length is of course a valuable tuning option by increasing or decreasing engagement. Making sure the bow travels smoothly in its range of functional motion, assuring it doesn't drag on the underside of the GS arm. Noting the sear spring leaf's contact edges are beveled and polished for smooth action as the trigger is pulled through pre-travel to stopping at overtravel. The greatest value of the TR is it simplifies the sear prep, maintaining a very close to same action as the traditional hammer sear relationship at holding and releasing the hammer reliably. The disconnector can be a source of a creepy feel perfection of all contact points is needed.

LOG
 

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Discussion Starter · #12 ·
Undoubtedly the sear spring has always been responsible for the final pull weight, past what's needed for a dependable safe trigger no matter the final pull weight. Trigger bounce hammer follow and doubles are not tolerable and the result of changing the geometry from the original design of the sear primary being the 90 degree from the line passing through the pivot to the tip, and the hammer hook tip landing tip first on the primary having a polished radius on the tips. Changing the hook length is of course a valuable tuning option by increasing or decreasing engagement. Making sure the bow travels smoothly in its range of functional motion, assuring it doesn't drag on the underside of the GS arm. Noting the sear spring leaf's contact edges are beveled and polished for smooth action as the trigger is pulled through pre-travel to stopping at overtravel. The greatest value of the TR is it simplifies the sear prep, maintaining a very close to same action as the traditional hammer sear relationship at holding and releasing the hammer reliably. The disconnector can be a source of a creepy feel perfection of all contact points is needed.

LOG
You have listed many areas of focus for perfecting the trigger. All of which I agree with. Sear/hook engagement type is one of the many listed. TR does simplify sear prep. But it too has issues which I discovered in my solids modeling.

The radiused sear requires a key dimension of the hammer be greater then 0.064". That dimension is the distance from the 0.020" hook face to the sear pin center (it's the feature called out on the hammer drawing at 0.109'). If the dimension is less then 0.064" then the hammer doesn't land on the radiused sear at the hook corner. Instead the landing is roughly in the middle of the hook face. As the sear then rotates the radiused face slides against the hook face ever so slightly raising the hammer. Continued rotation of the sear causes the hammer to fall ever so slightly as the sear reaches the outer corner of the hook. Ever so slightly is indeed small. But so is the fall of a flat sear face. On my hammer the critical dimension measured 0.056"
 

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The radiused sear requires a key dimension of the hammer be greater then 0.064".
What is that "key dimension" or what does it reference? Not on my prints.

That dimension is the distance from the 0.020" hook face to the sear pin center (it's the feature called out on the hammer drawing at 0.109').
I am familiar with that dimension. It is to the hammer pin center, not the sear pin. It is common to find aftermarket hammers that differ from that spec. Just what effect it has depends on that and several other factors. Para Ordnance had their hammer hooks moved down relative to that spec by a considerable amount with hugh problems ensuing, but that by far wasn't the only issue with the hammer.
 

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I agree world class shooters can feel a difference. But what is the source of that difference? That is the question I'm trying to solve. My thought is it isn't in the sear/hooks geometry.

I'm going to be simplistic for the moment so we don't yet get lost in the weeds. If a 3.25# trigger at break is composed of 0.75# due to the mainspring acting on the sear/hook the remaining 2.50# stems from the left and middle fingers of the leaf spring. Let's say world class shooters can sense a rather tiny 0.2# (or 6%) variation. This variation is only important after take-up and just till break. Anything after break should be ignored just as the best shooters train themselves to ignore recoil.

A 0.2# variation in 0.75# is measurable (it's over 25%). Yet my solids modeling shows a reasonably well cut sear and hook will have a variation about 1/400th of that. A simple change in the coefficient of friction between sear and hook could be the source. But all forms of sear/hook geometry are equally effected. The distinguishing difference of the geometries is the amount of hook movement. Yet the movement is too small to generate a meaningful change in the mainspring force.
First bold section - it IS the geometry that creates the different feel in the trigger. While trigger qualities may be comparable the trigger character and mechanics are not. That is why some can feel the differences. Until you experience the difference you won’t be able to tell.

A positive engagement, for example, will yield a heavy hard pull (lighter sear leaf loads to compensate) without much “feel” to it.

Second bold section - A quantifiable measurement is just that. It doesn't indicate the feel a capable organic organism can assess. The primary to secondary transition can be finished to different textures using different number of strokes and stones.

I think the best thing to learn is sacrifice a sear and use a good loupe - minimum. Start with a positive cut on the sear and try it in the pistol. Dry fire at a target...smaller target. You will find every little nuance to the trigger given sincere effort. Then try a neutral and a negative angle. Experiment enough and you’ll discover a short sear doesn’t contribute to great pulls.

I use a Yavapai comparator from Brownells...one of the best learning tools out there.
 

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I have been doing trigger jobs on my various pistols, but mostly 1911 and STI 2011 gun builds. Often times the parts themselves may not be exactly in spec, so you have to be able to get the correct geometry for the sear nose and the hammer hooks. I like to cut the hammer hooks to .020" which will provide good sear and hammer engagement. Some gunsmiths will cut the length of the hammer hooks to .018" but there is more risk of hammer follow over time.

I always start my trigger jobs by cleaning up the trigger slots of the frame....any burrs need to be eliminated. I usually use a flat needle file with various sandpaper. Next, I insert the trigger, and make sure it is a good fit in the frame. I do not want a great deal of vertical "up and down play" when the trigger is in the frame. nor do I want the trigger pad itself rubbing heavily on the frame. I like and use my "Opt Visor" with magnifier and lights, to see the very fine detail work when doing trigger jobs..... ;) (y)

I prefer a trigger pad that has an over-travel adjustment screw to be able to eliminate excess over travel once the sear is released. Sometimes I may eliminate vertical play by using a center punch to stake the edge of the trigger stirrups on 4 points of contact .....If the trigger stirrups are too tight, I simply make adjustments to file down the points of contact. Once the trigger is fitted properly to the frame, I may have to stake the disconnector hole at the top of the frame. If the hole is too large, when the trigger is pressed, the disconnector may have excessive movement. If I stake the hole too much, I take a needle file to make a good fit with the disconnector that protrudes through the top of the frame.

I then prep the sear nose. Many gunsmiths prefer the Harrison True Radius sear jig, and I believe it is a great jig, but before John invented his TR sear jig, I have been using a 25 year old Tom Wilson Sear jig for many years, and still get the desired results. I use hard and soft sear stones, and polish the sear nose once I get the correct geometry with the hammer hooks.
I may have to take the gun apart numerous times until I get the optimal fit..... When I have the optimal results, I will dry fire the pistol......I will have a clean breaking, creep free trigger pull, that may break at 3.5 - 4lbs. To fine tune the trigger pull weight, I may adjust the 3-tine leaf spring. I will bend the leaf spring to lighten the tension of the left tine that rests on the sear leg, and the middle tine that rests against the bottom of the disconnector. For some guns, used in Action Pistol games, I often use reduced power loads. I may replace the standard 23# mainspring with an 18-19 lb. main spring. This will help to increase the slide velocity on light loads, since there is less force needed to cock the hammer. When the gun is test fired, I want the empty brass to eject roughly 3-4 ft. away and over my right shoulder since I am a right handed shooter. If I see the brass being ejected 8 or more feet away, I know the slide velocity is too fast, and need to make adjustments to the gun, or the power of the load used. For 1911 or STI 2011 9mm guns, I use a very long extended ejector, since many mags use spacers in the back of the mag to allow the shorter 9mm cartridge to sit closer to the front of the mag. Chip McCormick sells 9mm "front ramp" style mags that work fine, and don't use spacers in the mag.....and the "front ramp" style mags helps to eliminate bullet nose diving for 9mm rounds......
 

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Discussion Starter · #17 ·
What is that "key dimension" or what does it reference? Not on my prints.



I am familiar with that dimension. It is to the hammer pin center, not the sear pin. It is common to find aftermarket hammers that differ from that spec. Just what effect it has depends on that and several other factors. Para Ordnance had their hammer hooks moved down relative to that spec by a considerable amount with hugh problems ensuing, but that by far wasn't the only issue with the hammer.
Sorry I mis-typed. I meant to say hammer pin center and you caught my mistake. Thanks. However I stand by my number the distance needs to be 0.064 or greater for the TR cut sear to not raise or drop the hammer hooks
 

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I have been doing trigger jobs on my various pistols, but mostly 1911 and STI 2011 gun builds. Often times the parts themselves may not be exactly in spec, so you have to be able to get the correct geometry for the sear nose and the hammer hooks. I like to cut the hammer hooks to .020" which will provide good sear and hammer engagement. Some gunsmiths will cut the length of the hammer hooks to .018" but there is more risk of hammer follow over time.

I always start my trigger jobs by cleaning up the trigger slots of the frame....any burrs need to be eliminated. I usually use a flat needle file with various sandpaper. Next, I insert the trigger, and make sure it is a good fit in the frame. I do not want a great deal of vertical "up and down play" when the trigger is in the frame. nor do I want the trigger pad itself rubbing heavily on the frame. I like and use my "Opt Visor" with magnifier and lights, to see the very fine detail work when doing trigger jobs..... ;) (y)

I prefer a trigger pad that has an over-travel adjustment screw to be able to eliminate excess over travel once the sear is released. Sometimes I may eliminate vertical play by using a center punch to stake the edge of the trigger stirrups on 4 points of contact .....If the trigger stirrups are too tight, I simply make adjustments to file down the points of contact. Once the trigger is fitted properly to the frame, I may have to stake the disconnector hole at the top of the frame. If the hole is too large, when the trigger is pressed, the disconnector may have excessive movement. If I stake the hole too much, I take a needle file to make a good fit with the disconnector that protrudes through the top of the frame.

I then prep the sear nose. Many gunsmiths prefer the Harrison True Radius sear jig, and I believe it is a great jig, but before John invented his TR sear jig, I have been using a 25 year old Tom Wilson Sear jig for many years, and still get the desired results. I use hard and soft sear stones, and polish the sear nose once I get the correct geometry with the hammer hooks.
I may have to take the gun apart numerous times until I get the optimal fit..... When I have the optimal results, I will dry fire the pistol......I will have a clean breaking, creep free trigger pull, that may break at 3.5 - 4lbs. To fine tune the trigger pull weight, I may adjust the 3-tine leaf spring. I will bend the leaf spring to lighten the tension of the left tine that rests on the sear leg, and the middle tine that rests against the bottom of the disconnector. For some guns, used in Action Pistol games, I often use reduced power loads. I may replace the standard 23# mainspring with an 18-19 lb. main spring. This will help to increase the slide velocity on light loads, since there is less force needed to cock the hammer. When the gun is test fired, I want the empty brass to eject roughly 3-4 ft. away and over my right shoulder since I am a right handed shooter. If I see the brass being ejected 8 or more feet away, I know the slide velocity is too fast, and need to make adjustments to the gun, or the power of the load used. For 1911 or STI 2011 9mm guns, I use a very long extended ejector, since many mags use spacers in the back of the mag to allow the shorter 9mm cartridge to sit closer to the front of the mag. Chip McCormick sells 9mm "front ramp" style mags that work fine, and don't use spacers in the mag.....and the "front ramp" style mags helps to eliminate bullet nose diving for 9mm rounds......
John Harrison did not invent the TR sear jig nor the TR sear treatment. The sear shape was collaborative and the eureka moment happened on a thread on 1911 Pro forum. The jig was designed and produced by Chuck Warner.
Joe
 

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Haven't tried a true radius. But I was setting them up so the primary is parallel to the hammer hooks. There was actually a thread not long ago about that. With this latest build, I didn't do that. I set it up the way the drawings showed. There is definitely a difference. It went from a little bit of creep to zero creep. None. This is the first trigger I've ever felt that had absolutely no creep.

The drawings were provided by jolly and backed up by Log. I believe Magnumite was the catalyst. Anyway, it totally worked.
 

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Discussion Starter · #20 ·
First bold section - it IS the geometry that creates the different feel in the trigger. While trigger qualities may be comparable the trigger character and mechanics are not. That is why some can feel the differences. Until you experience the difference you won’t be able to tell.

A positive engagement, for example, will yield a heavy hard pull (lighter sear leaf loads to compensate) without much “feel” to it.

Second bold section - A quantifiable measurement is just that. It doesn't indicate the feel a capable organic organism can assess. The primary to secondary transition can be finished to different textures using different number of strokes and stones.

I think the best thing to learn is sacrifice a sear and use a good loupe - minimum. Start with a positive cut on the sear and try it in the pistol. Dry fire at a target...smaller target. You will find every little nuance to the trigger given sincere effort. Then try a neutral and a negative angle. Experiment enough and you’ll discover a short sear doesn’t contribute to great pulls.

I use a Yavapai comparator from Brownells...one of the best learning tools out there.
You make many good points. Feel is subjective thus must be experienced. It is wrapped-up in the organic response. Cutting a sear for positive then moving to negative is a good test. Maybe I'm being to analytical. However I'm not letting my thinking allow a sear to be mis-cut by 10 deg.
 
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