Increase Trigger Pre-travel ?

[Jim Bellino]

Does anyone know of an accepted way to INCREASE trigger take up a small amount that doesn't involve purchasing several different triggers in hopes of finding one with a slightly shorter bow. Current installed trigger is is a short Greider with no take up tabs on the bow. I'm looking to gain approx .020 more take up for functional reasons.
Thanks,

[Jim Bellino]

Anybody????? I'm sure it's done a lot with the amount of aftermarket triggers people install.

[niemi24s]

Cut the forward, circular end of the trigger channel another 0.020" farther forward.

[mikeydio]

To increase trigger pretravel, I have reduced the thickness of the sear legs by removing metal from the back where it contacts the disconnector pads. I use Cylinder and Slide sears that have about .020" thicker sear legs than others. I only needed to remove .010" to pass the half cock test. C&S even recommends this in a supplement to their included instructions.

The method I used is to grind the material with Dremel 1/2" sanding bands using progressively finer grit. I use a Foredom tool with the handpiece firmly secured to the bench in a special vice and move the sear legs across the rotating sanding band. Final finish the job by pushing the sear legs across aluminum oxide stone and then finer to ensure they are flat and even thickness. To check for even thickness use your dial calipers because the jaws are ground parallel.

I have installed 10 C&S sears this way and while time consuming, it works, and each pass the half cock safety test.

Go slow.

Mike

[log man]

There is a limit as to the amount of pre-travel a gun can have, but what's important is that the half cock notch can be fully engaged without putting the trigger in a bind. Normally that is somewhere between ,040"-.060". To check pull to half cock and the trigger should not feel tight, or a more definitive check is to pull the trigger back while you pull the slide back just far enough to engage the half cock notch and release the slide to battery. Now release the trigger and it should reset.

If this is not the case I've had success in increasing pre-travel when needed by perfecting the fit of the trigger, the sear and the disconnector. First make sure that the trigger is as far forward as possible and the stirrup is flat and polished.

Then are the ears of the disconnector equal and the back or area of the disco that touches the stirrup flat and polished, also the top corner of the disco ears should be broke ever so slightly and polished.

And then the sear legs can be reduced on the side that contacts the disco, they must remain equal also, polish the bottom of the sear legs, the corner that the disco rides by and the area the rests against the disco ears.

LOG
_

[Jim Bellino]

Thank you gentelmen.....my question has been answered and I will proceed as you outlined by removing material from sear legs.

[niemi24s]

Began to wonder how much pre-travel a mid-spec U.S.G.I. M1911A1 would have and after a bunch of calculations came up with:
http://i129.photobucket.com/albums/p232/niemi24s/P089270002e.jpg
Because the disconnector pivot point is at the top of the frame (almost an inch above what's shown in the drawing), I think the pretravel would be quite close to the 0.062 inch distance shown.

Although it seems like a lot, perhaps JMB wanted to give the itchy trigger finger something to do.:D

[Jim Bellino]

Another great drawing, Dan....glad to see you are keeping busy! Did manage to increase pre-travel now 1/2 cock fully engages and disco resets.

[niemi24s]

Thanks Jim:....glad to see you are keeping busy!
Too busy, what with nearly 50 calculations using almost 30 specs for 5 different parts. Keeps me off the streets and out of the bars though. :D

Cheers

[Tom]

Keeps me off the streets and out of the bars though.
And that is always a good thing! LOL

[niemi24s]

The 0.063 inch figure for pre-travel given in Post #7 was partially based on one assumption that turned out to be a bad one. Went nuts trying to figure all the angles, etc., after correcting that goof and finally resorted to a 10X actual size physical model of the slide, frame, disconnector, sear & trigger.

Careful placement of the model disconnector showed the amout of pre-travel to be closer to 0.070", and shown below:
http://i129.photobucket.com/albums/p232/niemi24s/PA010003c.jpg
The model parts were carefuly laid out with a 1/100 inch graduation rule and my estimate of the real-life accuracy of the dimensions read off the model are probably within ± 0.002 or ± 0.003 inch.

F'rinstance, using the 1/100" rule, the disconnector nose protrudes about 0.042" above the top of the frame and the overlap/engagement between the disconnector paddle and sear feet is about 0.026" at first contact.

Kinda reminds me of playing with paper dolls as a child - the other kids, that is - not me! :D

Cheers

[log man]

Whoa, nice job on the disco, how about the sear and hammer, we want to see them at a 10-1 scale for a really complete picture. .070" should be ample pre-travel for half cock and reset function, nice to know that is what was built into the specs.

LOG

[niemi24s]

One thing the mock-up made real easy to see is how close the disconnector is to intruding into the magazine well when the gun's in battery, trigger not yet pulled:
http://i129.photobucket.com/albums/p232/niemi24s/P08A010002d.jpg
It's hard to see in this pic, but the rounded corner by the disco's "square" hole is just about flush with the forward surface of the mag well partition.

The sear feet position (highlighted bluish in the pic) was known from some calculations done last year, so no need to make paper doll sear & hammer.

A few other things easily found with the mock-up:

• The lower edge of the disco is just barely in contact with the trigger stirrup. That's why the "square" hole is up against the aft surface of the sear pin and the disco's upper end is against the aft surface of the frame hole.

• An aftward slide movement of about 0.065" is sufficient to cause disconnection.

Regards

[log man]

The disco protruding is an area to always check as the mix of parts can cause a problem. I always check after doing any trigger work by cocking and then sliding a mag up the well with the the bottom of the mag pushed forward so as to scrap the back wall of the well with the mag in an attempt to touch the disco. Haven't found one yet, but some look pretty close.

The point of the full size sear and hammer to scale is in regards to this thread, as it would show how the amount of pre-travel has an effect on the ability of the sear to fully engage the half cock notch and still have room to reset. I've found that the square hole in the disco on a few have had to be relived on the back side so as to be able to reset while in the half cock. This allows the disco to come closer to the mag well, but they weren't going far enough to begin with. Once in a while you'll see this, when you feel a trigger that has a little free travel of the trigger before it picks up the disco and then has pre-travel to the sear feet. This condition adds to the possibility of trigger bounce induced hammer follow.

LOG

[toolman]

The disco protruding is an area to always check as the mix of parts can cause a problem. I always check after doing any trigger work by cocking and then sliding a mag up the well with the the bottom of the mag pushed forward so as to scrap the back wall of the well with the mag in an attempt to touch the disco. Haven't found one yet, but some look pretty close.
LOG
I went through this recently after installing a new medium length trigger. The new trigger must have a short trigger bow because the disco protruding into the mag well had never been a problem until installing the new trigger. I can certainly see how a to-long trigger bow might not allow enough take-up.

[niemi24s]

The point of the full size sear and hammer to scale is in regards to this thread, as it would show how the amount of pre-travel has an effect on the ability of the sear to fully engage the half cock notch and still have room to reset.
OK, now I see what you're getting at. Sear & hammer will be easy.

Started thinking about a grip safety too, after reading your post. That'll be a lot more complicated cuz the MSH/frame geometry needs to be figured out.

Be nifty to have a 10:1 mockup made of something more durable (like sheet steel or aluminum) but that's waaa-a-ay beyond my capability.

Cheers

[Jim Bellino]

Dan.....more great work....thx for following up on my PM.....FYI I did notice that the disco on my Ed Brown pistol was filed and relieved on the front flat to keep it from intruding into the mag well....something I checked for on both my pistols after doing work to increase pretravel. I'm starting to acumulate quite a file of your illustrations, Dan.
Thanks,

[niemi24s]

My hat's off to Jim Bellino for suggesting models of the sear & hammer be added to that of the disconnector in my 10X actual size mockup. Doing so led to the discovery and correction of two other errors. As a result of these two errors, the previous values of 0.063 and 0.070 inch for trigger pretravel were both way too large.

The newly revised (and, hopefully, final) value is about 0.035 to 0.038 inch.

This pic replaces the one in Post #7:
http://i129.photobucket.com/albums/p232/niemi24s/P08A040012c_cr.jpg
The 0.035 inch depicted above is based solely on calculations. It is nothing more than the distance between the two points indicated, and does not consider that the disco pivots about its top end in the process of getting moved back to contact the sear feet. This value agrees reasonably well with that measured on the large scale mockup. This pic of it replaces the one in Post #11:
http://i129.photobucket.com/albums/p232/niemi24s/P08A040008a_cra.jpg
When the distances on the mockup are measured with a 1/100" rule, the total pretravel comes out to about 0.038 inch: about 0.002" before the stirrup contacts the disco and another 0.036" before the disco swings back and contacts the sear feet.

Don't have a USGI 1911 that hasn't been tinkered with to check this against, but at least both methods agree fairly well.

Does 0.035 to 0.038 inch sound more reasonable that the previous 0.070 inch?

[log man]

The .035" in full cock seems reasonable, but the point is how much is required to still be able to reset when in the half cock position. I found that in 10- 1911s that .032" to .050" of pre-travel measured at full cock to be required for the half cock to be able to reset. Slide in battery trigger back pull slide far enough to engage the hammer in half cock, release slide, release trigger and it should reset.

LOG

[niemi24s]

In this mockup of a mid-spec gun the disco may or may not reset.

The tops of the disco paddle's "wings" (or whatever they're called) overlap the bottom of the sear feet by about 0.002 to 0.003". There's about a 0.004" gap between the bottom of the disco and the stirrup with the "square" hole against the back of the sear pin and the disco upper end aftward against the frame hole.

This is with perfectly sharp corners on the interfering parts of the disco & sear, and the blueprints don't specify any chamfer or radius there that I can find.

Not sure if a 0.002 to 0.003" overlap would positively preclude reset in a real gun. And, that's about the same as my accuracy estimate for this contraption.

Could be some radiusing on the upper, aft corners of the disco paddle "wings" would help a bit. At least I don't see what harm it would do.

Keeping in mind my 40+ year association with the 1911 has been as a Bullseye shooter, I have a dumb question: what are the consequences of a disco that won't reset at half-cock?

Cheers

[log man]

Now, that's a very good question and one that I have to make a conclusion for, as this is a rather obscure area of the function that is rarely employed in normal operation. If the pre-travel isn't great enough for the trigger to reset in the half cock position, for one, requires that the hammer be pulled back to the point that it will reset so as to lower the hammer. Admittedly this may or may not make a bit of difference, but in the most remote of situations. Two and the area that I feel further justifies the adjusting of the pre-travel to the point that it does reset, is that just shy of that, the sear is being stressed as it isn't fully engaging in the half cock. Not good, as the sear nose is sitting right on the edge of the ledge, of course going to half cock in normal operation isn't a good thing either.

For smooth operation and short reset,(as long as the over travel screw is set correctly) breaking the top corners of the disco that has to bypass the sear legs to engage, and polishing the bottom and corner of the sear is a definite improvement and discussed in J.K.'s manuals.

LOG

[niemi24s]

. . .the sear nose is sitting right on the edge of the ledge, . . .
From this, I infer you're talking about a hammer with a non-captive half cock "notch".

The only ones I'm familiar with have captive half cocks - just like in the Army blueprint. I don't think the sear nose can be on the edge of this style of half cock because it really doesn't have an "edge" in the literal sense. The "edge" has a 0.012 to 0.017 inch radius, and would probably cause the sear nose to squirt forward and release the hammer if the aft corner or the sear nose got into the radius a little bit. Kind of like this:
http://i129.photobucket.com/albums/p232/niemi24s/P08A050005a.jpg
Do non-captive half cocks have sharp corners, or do they have a radius?

[Jim Bellino]

Dan...I do know of a recent instance a fellow forum member had that was with a pistol with the half cock notch (not shelf) that without enough pre-travel the sear would sit on the edge(nose) of the hammer 1/2 cock notch and the disco would not reset. any pressure on the trigger would cause the hammer to fall.
1/2 cock test that Log is refereing to was recommended by another long time bullseye shooter, who used to frequent the various forums ,but has not been active in almost a year. I believe his justification for this type of test is that if it passes with disco resetting you can be pretty darn sure you are fully engaged in 1/2 cock notch. Thats my take on it.
.038 for pre-travel sounds reasonable as both my pistols needed .042-.045 for proper function.
Nuther question for ya..(gotta keep you out of the bar). With hammer in full cock position approx. how much(if any) clearance should there be between the front of the hammer strut and the rear of the sear spring....more specifically, the center leg of the sear spring? This relates to a problem I just encountered yesterday. I'll give you a couple of three days to work that one out. Oh and did I mention your research and calculations have been most helpful as I cannot get all my questions answered from K's vol. I & II.

[berkbw]

Funny - everybody cuts on the hammer hooks, nobody ever cuts on the 1/2 cock.

[log man]

From this, I infer you're talking about a hammer with a non-captive half cock "notch".

Either way, I have both available and the non-captive does have a corner, some captive styles are pretty sharp and I tend to polish them a little smoother as it makes me cringe thinking about the sear nose hitting it. The point to further grasp is that if there isn't enough room to reset in the way it would while operating, means that if you pull the hammer back with your thumb the sear will not be able to fully engage as the disco is in the way and sits on the corner of the notch. Just not mechanically correct.

While I do believe this is the correct way to check and adjust pre-travel as I have discussed this with tech service at some of the manufactures and got an agreement from them, one said that if it didn't work it would still "probably" slow the hammer down enough not to fire.LOL As I've said before in 10-1911s I found .032"-.050" to be enough to function properly. The difference can be attributed the notch being deeper in some hammers then others. And once understood isn't hard to attain.

Does it matter, can only be guessed, as to how often does a gun go to half cock,let alone in a life threatening way. For many they wouldn't have known the difference if the half cock notch was ground off as it has never come into play.

LOG

[niemi24s]

The question of how much pre-travel is needed for disco reset when the sear nose is in the half cock notch is, I guess, answered by this line of thought:

If there's 0.038" of pre-travel when the sear's in the full cock notch but, say, 0.003" of overlap interfering with disco reset when the sear's in the half cock notch, then . . .

. . . if 0.003" was removed from the forward (as installed) surfaces of the sear legs (feet?) for an interference-free disco reset the . . .

. . . pre-travel would increase by 0.003" from 0.038" to 0.041".

[Keep in mind there's 0.002" between the stirrup and disco on my mockup which is included in the 0.038" of pre-travel. Also, all these distances are from a 10:1 scale mockup - not a real gun]

Does that line of thought make sense? :confused:

[log man]

Yes, that would be mathematically correct, perhaps an extra.001" for ease of resetting. The point that's come out from all this is the number is the result of proper function and is consequential. The correct number is going to vary from gun to gun.

LOG

[niemi24s]

Funny - everybody cuts on the hammer hooks, nobody ever cuts on the 1/2 cock.

Especially when (if the sear nose doesn't go forward after releasing the hooks) contact will be like this - with 0.030" hooks:
http://i129.photobucket.com/albums/p232/niemi24s/P08A050006b.jpg
With, say, 0.020" hooks the sear nose would be 0.010" right of what's shown. I'd think a trigger adjusted for zero overtravel would lead to some serious damage to the sear nose - at least ruin a good trigger job.

[log man]

I'd think a trigger adjusted for zero overtravel would lead to some serious damage to the sear nose - at least ruin a good trigger job.
Good illustration of that point. A relief cut on the sear will help some but it will still get hammered.

LOG