A look at the Bergara trigger internals. + tuning options

[22lfb]

Since I am very happy wit the Jewell trigger in my B14R, I felt confident enough to grind away the rivet heads and open the stock Bergara trigger to have a look inside.

The first picture can be used as a reference, second picture I assembled the top trigger spring the wrong way! Anyway, this is what we get after removing the (riveted) cover plate:

So apart from polishing and maybe different springs, not much to be done. But it also shows why Bergara can confidently say it's safe to remove the adjustment screw for the pull weight. It still acts on the trigger and there are two springs working against the trigger anyways.

The second thing - which was a bit surprisin to me - is that there are two holes pre-drilled in the trigger housing!

^number one could be threaded and then used to adjust the sear engagement!! I am rather surprised to see that it's there but not used. Maybe they went for the safe option somewhere during development to have a "lawyer freindly" trigger? I don't know. But putting an adjustment screw there would greatly increase the adjustability of the factory trigger.

The second hole:

This would make a nice trigger stop.

If i feel the urge I may try to find a way to put this back together, however drilling & tapping these holes does NOT require the trigger to be disassembled like this! And as always; if you do any work on your trigger make sure the gun is still safe afterwards!!

Though this could be interesting enough for some folks who do not want to spend the money on a new trigger right away... I know I would have tried this first, had I looked at it closer before ordering a Jewell

Cheers!

 

[Changed]

What are the odds that you can improve the engagement of the top seat and cocking piece?

 

[AirGunShawn]

At first glance in photo number one, it looks like you may be able to incorporate a spring in front of the set screw to counter act
some of the factory torsion spring making the trigger pull lighter. I imagine a full dog type set screw with a light spring around the dog point or a set screw with a spring pocket in it. That would balance the torsion spring and adjust sear engagement. And in photo two you may be able to use a compression spring or spring plunger in the hole and do away with the torsion spring all together. It looks like a fun project to tinker with. If you screw it up you just buy a new trigger like you wanted to begin with. These are my wild concepts and not to be considered instructions.

 

[AirGunShawn]

Since I am very happy wit the Jewell trigger in my B14R, I felt confident enough to grind away the rivet heads and open the stock Bergara trigger to have a look inside.

The first picture can be used as a reference, second picture I assembled the top trigger spring the wrong way! Anyway, this is what we get after removing the (riveted) cover plate:

View attachment 7726649

So apart from polishing and maybe different springs, not much to be done. But it also shows why Bergara can confidently say it's safe to remove the adjustment screw for the pull weight. It still acts on the trigger and there are two springs working against the trigger anyways.

The second thing - which was a bit surprisin to me - is that there are two holes pre-drilled in the trigger housing!

View attachment 7726651

^number one could be threaded and then used to adjust the sear engagement!! I am rather surprised to see that it's there but not used. Maybe they went for the safe option somewhere during development to have a "lawyer freindly" trigger? I don't know. But putting an adjustment screw there would greatly increase the adjustability of the factory trigger.

The second hole:

View attachment 7726652

This would make a nice trigger stop.

If i feel the urge I may try to find a way to put this back together, however drilling & tapping these holes does NOT require the trigger to be disassembled like this! And as always; if you do any work on your trigger make sure the gun is still safe afterwards!!

Though this could be interesting enough for some folks who do not want to spend the money on a new trigger right away... I know I would have tried this first, had I looked at it closer before ordering a Jewell

Cheers!

From your photos, it's not clear what the upper right hand spring does. Is it in it's proper position? I mean, did you go back and put it back into it's correct position? It looks like the lower right is the trigger spring. I'm sure it will be obvious when I crack her open like a pistachio.

 

[22lfb]

Top right spring nests in the little recess in the housing, it's held there by the cover plate. Without cover plate in place it pops out...

^This is correct! Top right resets the trigger, top left resets the sear, big spring in bottom is for pull weight. And as said - no need to remove the cover plate to add adjustment screws. The cover plate is rivettet in place! The rivets also hold the internals in place. I only removed it for demonstration purposes!

 

[AirGunShawn]

It's crystal clear now. The lower right hand corner has a M4 set screw under the torsion spring's anchored end. The screw has a protrusion similar to a dog point set screw. That keeps the spring wire contained between the protrusion and the trigger housing. It looks like yours is removed as is mine. I agree with you that there is no need to disassemble the unit to tap the rear side hole. They make special taps that pull the material out of blind holes instead of pushing it forward. They look a lot like a cork screw with cutting teeth. I'm going to pick up one of those in the bottom tap configuration and play with the unit a bit. It looks like you could tap as large as M4 x 0.7 or #8-32. You may nick the housing and cover plate but I don't see that as an issue even if you took the unit apart at a later date.

Top right spring nests in the little recess in the housing, it's held there by the cover plate. Without cover plate in place it pops out...

View attachment 7727225

^This is correct! Top right resets the trigger, top left resets the sear, big spring in bottom is for pull weight. And as said - no need to remove the cover plate to add adjustment screws. The cover plate is rivettet in place! The rivets also hold the internals in place. I only removed it for demonstration purposes!

 

[Criver600]

It looks like you could tap as large as M4 x 0.7 or #8-32.

#4-40 works perfectly

 

[AirGunShawn]

The hole starts out at about .102" and steps down to about .095 which is about .008" loose for a #4-40. Still, it will work fine.
BUT.... I don't want to install a set screw to simply limit the sear engagement just to end up with a short throw heavy trigger, I want to try some things that are a little more tricked out than that. If I were to install a long nose spring plunger, I could counteract some of the factory torsion spring force with the moving plunger nose and the body would act as a sear limiter.

Take a look at McMaster Carr #8495A11, 12 and 19. They are #6-32 long nose plungers with different spring rates and they have nylon locking elements to prevent them from moving once installed. The spring nose would push against the trigger blade and the plunger body will act as a stop.

Try this test.... stick a Allen wrench or something into the rear trigger hole and push it forward with some force and simultaneously pull the trigger. What you will feel is a reduced trigger weight.

You may recognize the parts in the photo as being AR-15 parts. They are about 3.86mm in diameter so if you opened the hole to 4.0mm they may work perfectly. If you went back to McMaster and looked up compression springs # 9657K611, 12 and 13, the same springs used to do a
CZ 457 trigger job, you could see the different rates for them. They could be contained with a M5 set screw. There is only about .56" in hole depth so my feeling is the self contained plungers are a much better place to start. I even thought of replacing the AR-15 plunger with a simple 4mm ball bearing. That will buy me about 3mm of useable hole depth. I know the bigger tap will likely break out on it's sides at some point but it wont matter if I do it carefully.

My thought was to do something super simple so anybody could tap the hole and install a plunger and have a better trigger. It wont be a Bix-N-Andy but it will be a $20.00 improvement. Is it safe?? All it would do is reduce the trigger weight and shorten the sear engagement. Determining it's safety would be in the hands of the owner just like every adjustable trigger is once dialed in.

I'm not suggesting anyone do this, I'm just thinking out loud and there are internal things to consider like the spring loaded ball bearing that catches the safety lever. I will be happy to share my blunders and save you the grief, probably by 10/30/21

Again.... just my dumb ideas.

 

[AirGunShawn]

I will end up with a #6-32 tapped hole to test out my plunger concept but I decided to test out the #4-40 just for fun. I used a chip clearing tap that has a 3-5 imperfect chamfered cutting threads at the beginning of the tap to see if that would cause problems for people. There was still enough clearance inside the trigger to allow the taps full threads to be cut in the housing to allow the set screw to be installed. That means you don't have to have a bottom tap or a chip clearing tap which would be the ideal. The spiral flute design on a chip clearing tap pulls chips back out of the hole, so chips won't accumulate in closed-end holes or inside your trigger. Your average tap that people have pushes the chips forward. For the test, I tapped the trigger upside down and removed the tap often to clear the chips out of the hole. If you go to McMaster-Carr and search for #2529A44 you will see the ideal tap I'm describing. Besides pulling the chips out of the hole, that tap is a bottom tap so it has very few chamfer threads on
it's tip.
My point here is to let people who are only vaguely familiar with taps that they should have no trouble installing a #4-40 set screw and that change
alone makes a substantial improvement. I turned the screw in until the firing pin fell and then backed it out by 90* which equals .006"

EDIT: There is a gap between the housing and the trigger so you should get a .25" long set screw if possible. I have an .12" screw in
mine now but I can feel it's nearly ready to fall inside of the unit.

The plunger concept does work but I need to work out the spring force so the trigger can re-set. The long nose plunger may turn into a ball plunger with a shorter stroke to capture reduced trigger weight and to allow for adjustable sear engagement.

 

[Criver600]

makes a substantial improvement.

I agree. If you halfway understand how triggers work its an easy low cost mod.

 

[AirGunShawn]

Semi related query.... I asked our local club director if altering my B14R trigger would kick it out of the stock class. He said
not at our club. How do other clubs view altered equipment? My Vudoo is still in the factory class. That seems crazy.
My first time at the club my bone stock Bergara stomped on the directors newly purchased used V22.
I had to laugh silently.... As an added insult he thought I was shooting SK yellow box.

 

[AirGunShawn]

I pulled some set screws from McMaster-Carr for you to reference if your not familiar with the various set screw tip styles. The ideal
set screw would have hemi-spherical tip but that isn't offered with a nylon locking element. So I will be going with one that does
like #91385A106. Below are some examples of set screws you may want to look into.
If you search for #91385A106 you will see most of the set screws they offer in #4-40 x 1/4" long. These are jumping off points to
get you started. If you poke around you can see all of the inventory. The SS is a little softer than the carbon screws.

I also included some illustrations of two different tap styles. The first one pulls the chips out of the hole being tapped and the second pushes the chips forward. The ideal tap is the first spiral flute tap since you don't want to take the trigger apart or have chips go into the trigger. I used the second tap style today by tapping some threads while the trigger hole was facing toward the ground and removing the tap and chips every three complete revolutions. I suggest you use a bottom tap to achieve full threads. You can see in the second photo that the first few threads don't cut to the full depth. So if you don't use a bottom tap, your set screw may have trouble getting to the trigger blade. Also get two flute taps so they can be measured once the printing gets worn off. Three flute taps cant easily be measured without a special micrometer because of their triangle-ish shape. I know.... way more information than you want or need.

#2529A56 ~ Tap one.
#2523A413 ~ Tap two.

#91385A106 ~ BLK cup point with nylon lock element.
#92695A112 ~ Male cone point.
#92778A047 ~ Oval point.

 

[AZ Dan]

I've got one of the new BMR's on order, should be here sometime next week. My intention was to replace the trigger entirely, but I am going to try your method with set screws. A simple and cheap sub $10 fix is preferable to a $240 fix.

 

[E. Bryant]

Awesome thread - I'm impressed by the ingenuity and willingness to dive in and explore options for improvement.

A simply cautionary statement seems necessary (not so much for those actively participating, but rather the passive reader who may stumble across the thread now or in the future) - be careful when modifying features such as sear engagement surfaces on PM & MIM parts. You don't know if they are hardened to full depth (most aren't), and aggressive material removal combined with adjustments that decrease engagement might result in some not-so-fun surprises at a later date. Go gentle on any stone work; anything more than a few swipes to remove burrs may be too much.

If someone has already confirmed via proper measurements that these parts are fully hardened, the above warning may not apply.

 

[ma smith]

Awesome thread - I'm impressed by the ingenuity and willingness to dive in and explore options for improvement.

A simply cautionary statement seems necessary (not so much for those actively participating, but rather the passive reader who may stumble across the thread now or in the future) - be careful when modifying features such as sear engagement surfaces on PM & MIM parts. You don't know if they are hardened to full depth (most aren't), and aggressive material removal combined with adjustments that decrease engagement might result in some not-so-fun surprises at a later date. Go gentle on any stone work; anything more than a few swipes to remove burrs may be too much.

If someone has already confirmed via proper measurements that these parts are fully hardened, the above warning may not apply.

Looking at those internals doesn't give a ton of confidence they are fully hardened machined parts, etc

Is the Tikka or some other good trigger out there -- is it that rough inside when fully dis-assembled?

 

[AirGunShawn]

I got my #6-32 long nose plunger, McMaster-Carr #8495A11 installed into my trigger and after it's initial adjustment I'm getting an 11 once pull.
The spring nose counteracts a substantial portion of the trigger torsion spring and the plunger body acts as a sear limiter.
The factory states the high end weight to be #3-3 ounces and the low end to be #2-4 ounces. That's a a 79% decrease
from it's high end. The plunger has a nylon locking feature and costs about $5.00 I started by turning the plunger inward until
the firing pin fell and I back it out about 110*. Don't forget that there is a window in the side of the trigger unit to observe it's
sear engagement. Your not stuck with doing it by feel alone.

This is what I did and I feel it's plenty safe for me. I rock climb, Scuba dive and Hang-glide and feel I'm very safety oriented
but you will need to make every determination about all safety yourself.

I'm afraid that in my case it's not a lot of ingenuity.... I've designed automation and tooling for 30 years.
I do most of this stuff while I have a slight beer buzz on.

 

[AirGunShawn]

I suspect that the trigger, upper sear, springs and set screws are the only steel parts in the unit. I agree that all of the
parts appear to be PM or MIM. I however have faith that they will hold up just fine to the aforementioned modifications.
I will likely never open this unit up but when I do lap the sears of my triggers, I use 9 and 3 micron Aluminum Oxide PSA film.
The amount of material that gets removed is very likely under .0015". It's also done in the direction of travel to mitigate
any kind of micro interlocking between the sears.

Even If the sears were made from billet stock, I would expect them to be case hardened to a shallow depth of .015"/.030"
and not through hardened. All of those changes in cross sectional area would be prone to cracking. A short zap with the induction coil
in the sear area seems like the natural choice to me.

Just my opinion and not facts from talking to Bergara.

Looking at those internals doesn't give a ton of confidence they are fully hardened machined parts, etc

Is the Tikka or some other good trigger out there -- is it that rough inside when fully dis-assembled?

 

[AZ Dan]

I wish the 6-32 adjustment screw in front of the trigger would fit in the back after I tapped it...but there isn't enough meat on the bone to drill/tap for a 6-32. But a 4-40 tap fits very nicely in that hole. I had to order some 4-40 extended tip set screws from McMaster Carr, but I can wait until Tuesday...

 

[AirGunShawn]

I may have not understood AZ Dan's post.....

I have the rear tapped not for a 6-32. The front and the rear hole have the same thickness of material.

I hope you folks buy the set screws with the nylon retention patch. Tandem set screws work if you have the depth and I even tried them
in the 4-40 size as an experiment prior to tapping for #6-32. I noticed that once I got my trigger set precisely where I
wanted it, the second set screw had a tendency to upset it's position and twist it forward. That reduced the sear engagement.
I could have made it work, but I work on my guns much to often to tolerate any kind of back talk from them.

Some time ago I had glanced at the trigger and felt that I could tap as high as 8-32 or M5 as long as the trigger unit was riveted together
and if a later date I were to take the side plate off it would still be OK because the trigger has some small locating buttons
built into the left side housing. One is shown just below the light spot in this photo. Are you concerned your going to break
out of the left side housing and also into the right hand plate with your screw threads??

Since I loathe giving out bad information that I felt compelled to check my B14R trigger again today. There is a spot just forward
of the trigger blade where you can get a direct measurement of the dimension between the inner housing and the removable side plate.
The width is .176", and the different screw widths are as follows;

#4-40=.112"
#6-32=.136"
#8-32=.164"
-------------- break out line.
#10-32=.190" ( tap drill = .158" OD ) .007" break out on each side.
M5x.8= .196" ( tap drill = 4.2mm = .165" OD ) .010" break out on each side.

From my point of view, there is plenty of meat to use anything up to and including an #8-32 without any break out.
Even If I went up to M5, only the crests of the major diameter of the fastener would break out into the sides and then
only by .010" on each side.

I would however investigate the rear hole some more before I went bigger as there are some items like the safety ball detent
that need t0o be considered. Behind the ball, there must be some sort of spring. I suspect it's a flat leaf spring but I have not
opened my trigger up as of yet.

As a side bar, The second photo is the chip[s being pulled out of the hole when using a spiral flute tap, the third shows the chips
being pushed ahead of the tap. It is a spiral point tap ( plug chamfer ) but almost all taps push the unwanted trash forward.
In this case that is bad because the trash is going into the trigger housing.

Photo four is of a form tap and It has no cutting teeth at all. They can be tricky to use if you are not familiar with them but would be perfect in this application as you don't want chips and the metal is aluminum.
I used the spiral flute to align to the hole axis and then finished the hole with the spiral flute to withdrawal the chips. I could have
gotten a spiral flute with a spiral point but I wanted near perfect threads at the tap point to be certain that the set screw or
plunger would be able to advance far enough. So my tap was a spiral flute / bottom tap. #26255A52

Please let me know where I screwed up or if you simply want to give me your opinion.


Shawn Carroll
COMAU
Design / Check

 

[AZ Dan]

I tapped it 4-40...works perfectly, and that is as big as I am comfortable going. Looking at my trigger and referencing your #2 photo you posted, my trigger has about half the wall thickness at the 12 o'clock position, if you oriented the trigger as if you were shooting the rifle.

Also, I'm doing this on the new BMR....my stock B14R and the stock BMR triggers are different triggers, but they have the same blind holes.

The factory Bergara screw I took out of the bottom adjustment hole is 6-32, I believe. It is too wide to fit in the blind hole I tapped without risking break through. Keep in mind, I am not a machinist and don't have a mill or drill press, so tapping it 4-40 was the easiest option for me.

I completed my work, and I now have a 1lb trigger with passes a safety blow with a mallet and multiple hard hits on my bench.

 

[AirGunShawn]

There is a saying..... It say's; "that a man convinced against his will, is a man of the same opinion still"
I see your concerns but I just don't share them.

AZ.... By blind holes, I assume you meant the BMR trigger currently has simple clearance holes in the same locations but
need to be tapped??
I no longer have a mill either so I must do my work with a hand drill. I also do things in such a way that the average guy with
only a hand drill can do the work. Otherwise posting this would be a waste of my time. When I went up to a #6-32 tapped
hole, I progressively made the hole bigger to avoid creating problems for myself. The drills are only $3.00 each.
Are you saying the BMR and B14R trigger guts are not the same but utilize the same Remington 700 housing??

BTW.... the B14R trigger's rear hole has a stepped diameter. At about half way down it's depth, it's diameter
reduces by about .010" It's not much but by percentage on that small .112" tap it's a substantial amount. BEWARE!!
It will be very obvious if you use only a bottom tap with few chamfer threads.

I just checked the screw your talking about in the front, bottom of the housing and it's an M4-0.7 screw. (.157" OD.)
I have not taken my unit apart yet but It's my belief that the M4 screw that adjusts the spring tension has the long
nose on it to capture the spring between it's nose and the housing. That leaves the top shoulder of the screw
for the spring to rest on as shown in the sketch.

I zoomed up on the trigger photo by 21X and did some scaling. Based on that, the cross section of material above
the rear trigger hole is about .024" thick. So if I were to look at photo BT-1, you will note a thinning of the upper cross
section beyond the holes initial 58% of the holes depth. That's an estimation but even with a #4-40 screw, you already have
a partial break out in the final 42%. So that means that my #6-32 has .012" of an inch more break out than you do.
That extra break out is the same thickness as three of my hairs.
My plunger in it's final 42% is captured by something like 85% of it's diameter. Therefor my thread crests from
approximately 11 to 1 o'clock are partially or fully exposed.
Nearly 100% of the trigger spring load is being directed down the plunger axis and near zero force is being applied in an upward
direction on the plunger body.
This is a good time to point out that my plunger is about .020" longer than the hole is deep so I have tons of engagement
and support over it's entire length.

In photo's #4 and #5 you will see an example of threads that are only partially captured but do a great job. It is from
my Springfield 1922 M2 rifle. It has very small loads on it and under 40% of it's diameter is surrounding the threaded
adjustment rod. The bottom line is that it has proven to be perfectly adequate for it's application.

I have also added some photos about taps. In photo #6 the first is a straight flute bottom tap. It has few chamfer threads
on it's nose.
For this job you need complete threads or your screw wont be able to advance to the trigger. Second is a straight flute /
spiral point tap. It is great for through holes but observe it's 4-5 incomplete chamfer threads. Photo #7 shows the hole types
and the tap styles that are best suited for the job. Go back up to post #19 and look at the second photo. Take a good look at the
size and amount of the "Chips" that need to be removed from the hole. They are real and not some representation of chips.
If you use a straight flute / spiral point tap in a blind hole all of that material gets pushed down into the hole while you are tapping.
The net result can very easily be a broken tap that is very difficult to remove. Easy outs don't work on taps. I recommend two flute
taps for ease of extraction and measurement. 4 flute are OK but don't get 3 flute. Again, look how many imperfect threads you have
in photo #8 shown on the right hand tap. Any fastener will only go as far as your perfect threads will allow. Starting with one tap
type and finishing with a bottom tap is IMO the best way for the average guy to get this done.

Below is a good read on taps....

6 features of internal taps at a glance | RUKO

ruko.de

As a reminder.... When you tap a hole you are only getting about 75% of it's threads engagement. That still yields over 90% of
of a tapped holes strength in tension. In this context, engagement refers to how deep the teeth are biting into the tapped housing
sides and not how much length is being engaged. When it's required to get nearly 100% of the tapped hole strength in tension
you would need to get a 3 piece serial tap set. ( See Roku )
Trying to achieve the last 5 or 10% of tensile strength can be done in faster, simpler and cheaper way's. As I compose this, while
doing the work to achieve my FFA Light Sport Aircraft certification, I have no recollection of using serial taps. Still, they are used
on occasion by someone.

These are all just my opinions so you folks will need to evaluate the information on your own as to it's validity.

 

[WeeHooker]

Thanks to the OP for posting this.. It's nice to see inside the trigger! Great info. FWIW, I had already modified the factory trigger on both of my B14R's by adding the sear engagement screw with allot less info with some basic "how to" posted elsewhere. ( I figured if I gaffed it up, I'd just buy an aftermarket.) Anyway, It was an easy job, really. I bought the drill and tap set and a handful of 3/8"x 4-40 full dog set screws from THEBAY. Total investment was less than $20. I then drilled ( with a hand drill), tapped and installed without even removing the trigger from the action. There is really VERY little material that gets removed from that pilot hole. Here are a couple things I learned.
1) Hold the trigger shoe back with your off hand while drilling and tapping. It allows you to instantly feel when /if the tools break through and hit the trigger .
2) Use a tap that is designed for a blind hole or you can carefully grind the tip of a standard tap back 1/16" or so to allow it to fully thread the hole.
3) Drill and tap slowly and frequently back the tool out to clear out the hole of chips.

I'd say the first one took maybe 40 min. the second 20 min (including adjustments after the install.) Both triggers are now set at a consistent 20 oz and pass the bump test. I have a Timney Hit trigger sitting on the shelf should I change my mind but so far have been very pleased with the ease and results of this trigger job! I think this is a great option for those not needing /wanting a 8 oz trigger.

 

[HenryRed]

How does the mods compare to a aftermarket trigger?

 

[AirGunShawn]

Henry,

The short answerer is, I like it enough that I will never feel the need to replace it with an after market unit.

A really simple pre-test is to use a small Allen wrench or something and insert it into the existing rear hole.
As you apply force to the Allen wrench, your trigger will get lighter. It's the plunger body that contacts the trigger
blade that gives you precise control of your sear overlap. The small thing you put in the hole is going to drive into
your finger tip with about 5 pounds soooo.... You may want to protect your finger even if it is only a spent .22 case
over the thing you test the trigger with. See photo #7......

I just re-tested the B14R spring plunger modified trigger and would be surprised if you were not totally pleased with it.
It's not like my TTD 4 oz. in my Vudoo or my Annies 5098 6 oz. triggers but it cost $4.56. To be honest, I'm a trigger snob
and intolerant of trashy or even marginal triggers. It is plenty light and breaks very clean.

If you didn't like it, you simply remove it and your trigger is almost back to it's stock configuration.
Everyone else say to use a #4-40 set screw.... I absolutely disagree with them. The #4-40 shortens your sear engagement
and that makes the trigger feel nicer, but I think they are missing out on a valuable opportunity. That said, If you
have done #4-40 set screw you can still do #6-32 long nose spring plunger. Also, they don't make a #4-40 plunger.

The plunger has a spring loaded nose that acts as a counter balance against the factory spring. Therefor you can have
a safe and adjustable amount of sear engagement that also reduces trigger weight. I saw an opportunity to enhance the
trigger at very little cost that people could do at home. If it required grinding off the seven rivets, I would not even have pursued it.

The plunger allows you to get an 11 ounce weight with a safe and adjustable amount of sear. The plunger gives you control
over how much sear you want to have because it's nose is spring loaded and retracts into it's body. The trigger stops against
the plunger body and not the nose.
If 11 oz. is too light, there is a lighter plunger.

Most people say the #4-40 is perfect and the existing hole is perfect and that there is not enough meat for anything larger.
BS... Between the plates is .176" The #6 plunger is .136" OD. ( shown in image #4 )

btw... the factory hole actually has a stepped diameter. About half way in it reduces a few thousandths. That is going to
make it more difficult to tap. It should be .087" / .095" based on it's 2/3D to 3D. From memory the beginning of the hole
is over .10" Use some thin lubricant. A standard 3/32 drill would be a great size.

To get the lowest trigger pull you must also adjust or remove the adjustment screw in sketch #5 and photo #6.
It's a small special M4 screw that that traps the anchored end of a torsion spring. ( front, lower corner of the trigger. )

The spring plunger approach allows for longer engagement or sear overlap. You achieve the light pull because the plunger is doing
the majority of the work for your finger.

As a starting point, I adjust my plunger until the FP falls. Then I back it out by about 110* That should back it out by about .0095"
at the plunger tip.
( 32 threads per inch / 360* x 110* = .0095" )
If you measure the trigger, from the pivot to where the plunger contacts it and then from pivot to sear it is about 2.4 : 1
So .0095" at contact point x 2.44 ratio = .023" movement at the sear. The sear to trigger looks to be about 1.9.
So... .023" movement at the sear will be about .012" rearward movement at the center of your trigger finger.

I agree with points one ,two and three of post #22 but my description of point #1 differs. Don't pull the trigger back as normal but push it in it's opposite direction while drill and tap. You will feel it the moment of contact. There is no need to freak out when you touch the trigger with the drill or tap.... it is steel. If you over twist the tap it will however break !!

In really simple terms.... the trigger is a teeter totter. 100 pound girl on the left side with a 50 pound girl on the right.
If I add a 40 pound bag of sand on the right side, ( plunger ) they are close enough in mass to have fun.
The trigger has to have a slight bias to allow it to reset in any case. The FP spring is always trying to drive the upper sear downward
when the gun is cocked.

There is a sear viewing window in the trigger housing. I suspect that if some of these guy's looked at the sear they would find they
are on the hairy edge. My concern is this: If you zoom way up on photo #3 in post #21 and take a close look at the upper sear
it appears to have a slight radii. I would expect to have a dead sharp corner where the sears separate. That would also help
explain why some of these guys get 16 / 20 oz. triggers with only a set screw. If you did a quick search on vector forces you may
see how the trigger is holding but not truly safe. In my mind, reducing the sear should not decrease the weight from 36 oz. to 16 oz.
Something unseen is going on.

Pics one ,two and three are just tap types that show the direction the chips expelled. #3 shows the initial, imperfect threads
of most taps. Some guy's are using full dog set screws to get around imperfect threads. I used bottom taps and was more
concerned about the fastener backing out. I used plungers and set screws with nylon locking patches built into them.

 

[BLJ]

Tag

 

[AirGunShawn]

BLJ.... TAG?? I'm not current on the internet lingo.

Tag

 

[BLJ]

........for later reference

 

[AirGunShawn]

Maybe you all know this but I feel compelled to show this photo again since it's important but never gets the attention
that the flat BT-1 photo gets.
From it, you can see the true pivot points and sear. Image BT-1 is somewhat misleading because the pivot points are removed
and the parts have shifted. If your simply adding a plunger or set screw, you may not even care what the guts
look like other than passing curiosity. Photo number three is the real deceiver in terms of what is the sear because that square
block section, that is likely a crude & rude stop is shown on top of the trigger blade. The sear is the line indicated by the green arrow.

Just in case anyone cares......

 

[Enstromentals]

Maybe you all know this but I feel compelled to show this photo again since it's important but never gets the attention
that the flat BT-1 photo gets.
From it, you can see the true pivot points and sear. Image BT-1 is somewhat misleading because the pivot points are removed
and the parts have shifted. If your simply adding a plunger or set screw, you may not even care what the guts
look like other than passing curiosity. Photo number three is the real deceiver in terms of what is the sear because that square
block section, that is likely a crude & rude stop is shown on top of the trigger blade. The sear is the line indicated by the green arrow.

Just in case anyone cares......

Which weight spring plunger did you end up settling on?

 

[AirGunShawn]

I thought the McMaster Carr #6-632 ( 8495A11 with locking element ) was a good idea until I saw the trigger sears. Certainly it does counteract a lot of the factory torsion spring force and the body acts as an adjustable sear. But.....with the rounded sears, it is an unsafe practice to try and use. The #4-40 set screw is even worse because for it to have any effect, you must put the sears on the radii of the adjacent sear. ( less engagement ) This entire thread should be removed by the admin due to it's dangerous nature.
I spent 30 years as a designer for COMAU, I rock climb, scuba dive, hang-glide and I applaud cool, creative idea's. I'm telling you, this trigger
modification is a bad idea!! It has other pit falls that have not even been addressed.

 

[Enstromentals]

I thought the McMaster Carr #6-632 ( 8495A11 with locking element ) was a good idea until I saw the trigger sears. Certainly it does counteract a lot of the factory torsion spring force and the body acts as an adjustable sear. But.....with the rounded sears, it is an unsafe practice to try and use. The #4-40 set screw is even worse because for it to have any effect, you must put the sears on the radii of the adjacent sear. ( less engagement ) This entire thread should be removed by the admin due to it's dangerous nature.
I spent 30 years as a designer for COMAU, I rock climb, scuba dive, hang-glide and I applaud cool, creative idea's. I'm telling you, this trigger
modification is a bad idea!! It has other pit falls that have not even been addressed.

Why the sudden change of heart? Did you have some negligent discharges?

 

[AirGunShawn]

Why the sudden change of heart? Did you have some negligent discharges?

This is not a sudden change of heart. And to answere your question...no, I didn't have any NDs. I replaced the trigger before that happened.
I only shoot at home, so an ND would have made almost no real difference. It's stupid and an exercise in poor judgement.

Back in October of 2022 I was telling people to refrain from making the plunger or set screw mod. Below is a email to someone named Ken Smith.
I have helped many people with the CZ 457 trigger but it is a different animal all together. Anyone can do it successfully.
Look close at the dates of this thread..... It's January of 2022. Not 2023.
I put a Jewell HVR into my B14R but wish I would have installed a TTD like my V22 had.

Look close at the sear surfaces. How can anyone believe that they are going to have a safe crisp break with those rounded corners.
Do you feel that the sear will snap over that round edge??? What do you believe in your heart?

I have told people that the #4-40 set screw is a bad idea. They say that the trigger ""weight is reduced and they have not had a problem yet.""
YET is the key word. There is a saying. ""A man convinced against his will, Is a man of the same opinion still.""
I wish I could show you what a mouse trap condition that they have put themselves and others in. Actually, a Victor brand mouse
trap is a pretty good example of the rounded sears. Do you know how unpredictable those traps can be?? I truly hope that you can see
the problem for yourself. It was my cool idea but now I'm condemning it with all of my heart. What would make me change my position
in a public forum like this ?? I opened the unit up and saw the problems.

I have asked the #4-40 set screw guys how it lowers the trigger weight and none can give me an answere. Consider this.
The set screw advances the trigger blade increasing the torsion spring pre-load. Shouldn't that increase the weight a small amount?
If you look at the sears you can imagine them touching at the 6 o'clock position. And then as the trigger is pulled, the 5 o'clock position,
and then at some point.... BANG !! It will feel consistent and it's weight will be pretty repeatable. Do you know of any other trigger
that has rounded SEARS?? What does the #4-40 do to reduce the trigger weight?

People have added set screws to shorten it but I advise against that. The last image is of a spring plunger idea that
I came up with that would shorten the travel and over come most of the factory spring force. I did my trigger and had no issue.
Dan did his trigger and had problems. I spent many hours working with him and his trigger. I even bought
an extra to tear apart. After seeing the internals it became apparent that making a mod to the factory unit was folly !!
The guy's that think they have had success with a 4-40 set screw don't realize what danger they are in.
If your curious I can show you why. In short....the sears have rounded edges and they are barely hanging on the radii.
In my plunger concept, the body of the plunger did the same thing the set screw did..... the plunger nose neutralized
most of the factory torsion spring force. It worked great except the soft MIM trigger blade is too easily damaged by the
drill bit and tap by the average user.