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  #1  
Old 06-16-2009, 03:46 PM
TheOtherGoose
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Checking my understanding of the Buckmark's trigger...



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Pardon my crude drawing skills on this one...



Does this drawing reflect the relationship between the hammer and sear surfaces on the BuckMark? My drawing is obviously exaggerated and simplified for clarity (I hope).

I ask because, after reading some old posts on the subject, some firing system components said to "cam" when the trigger is pulled. Does the term "cam" refer to climbing an inclined surface on the hammer or sear? I assume the inclined surface (if this is so) prevents the hammer from being released by an accidental knock/bump. Is my understanding correct?
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  #2  
Old 06-17-2009, 11:04 AM
Maaso

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This picture might help...

(scroll down a bit)
https://www.rimfirecentral.com/forums...d.php?t=210545
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  #3  
Old 06-17-2009, 11:49 AM
TheOtherGoose
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Thanks for the link. Based on the picture in the linked thread, I now see that the situation is the opposite of what I had drawn. It appears that the sear has the inclined surface. I feel stupid...
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Old 06-17-2009, 12:16 PM
chim
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Don't let it bug you.
__________________
..............chim

Buck Mark Disassembly/Reassembly Page here:

http://chim.embarqspace.com/#
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  #5  
Old 06-17-2009, 01:12 PM
Heggis

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Actually can't remember how they are originally... The picture that is in that thread is picture of my "fine tuned" sear and hammer. I have taken a lot of material off from both. But you can check your guns fit by putting your hammer and sear "outside" to the pins so you see how your parts look.
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  #6  
Old 06-18-2009, 07:47 AM
LDBennett
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In most guns the hammer ledge that the sear engages is not on a radial line from the hammer pivot point but angled so that indeed the hammer has to cam rearward to allow the sear to fall off the hammer's sear engagement shelf. To eliminate that camming, the hammer's ledge has to be made closer to a radial line. But it you go too far several things can happen: The sear can fall off the hammer's ledge with a mere bump of the gun; stoning the ledge on the hammer can stone right through the hardened surface making the revealed metal on that ledge soft and very wear prone. This latter case is probable but not mandatory if the hammer is hardened all the way through and not just surface hardened, or after the stoning the surface hardening could be restored.

The bottom line is some camming of the hammer is mandatory for a safe gun but it can be made minimal and still maintain a safe gun.

As for creep reduction, there are many different ways to reduce the creep in the Buckmark but the one I like is called the modified Colt system (AGI master gunsmith Bob Dunlap's method). The edge of the sear that goes into the hammer ledge is chamfered at a 45 degree angle so that when the sear moves it hits the angled surface and the hammer forces the sear out of engagement. Colt 1911 owners will recognize this approach. The trick is the engagement before hitting the 45 degree chamfer must be no less than about 0.020 inches. Excellent feeling triggers are possible even with significant camming action of the hammer by the sear.

My Buckmark has reshaped sear spring legs (rather than the flip) and the chamfered sear and the trigger pull is near perfect. It is also nearly as safe as the original factory trigger setup and will wear as well as the factory trigger. But most importantly for home gunsmiths, it is easy to do well.

LDBennett
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  #7  
Old 06-18-2009, 02:17 PM
TheOtherGoose
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Excellent information, as always, LD. Thank you.

I took a look at the AGI website the other day and may spring for the trigger job video series. $600 does give me pause, though...
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  #8  
Old 06-18-2009, 03:51 PM
LDBennett
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TheOtherGoose:

You don't need to spend $600. That gets you trigger jobs for specific guns. The general purpose trigger job video (two DVD's) covers any gun you might ever run into as so many are similar and the principals are the same for most all commercial trigger systems. The AGI video is "Trigger Jobs Professional Course" AGI DVD #3054, a two DVD course, 8 hours long. It is a tutorial on how trigger systems work, how to modify them to make them work better, and perhaps ten example guns for the various types of designs of common guns. It is not cheap but is not $600, at least the last time I looked.

I have viewed mine at least 4 times completely through and applied the principals learned there to many guns. If I am going to take on a new gun I have never done before I will review the section of the DVD that applies but amazingly, most guns are similar to a couple of different trigger system designs and I rarely have to review anything but the general section, if at all.

Send me a Personal Message with your email address and I'll send you a synopsis of the AGI course that I wrote.

LDBennett
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Old 06-19-2009, 07:11 AM
LDBennett
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AGI Trigger Jobs course synopsis

TRIGGER JOBS ON HANDGUNS AND RIFLES:
(Single Action Part of Trigger Mechanisms)
By Lynn Bennett

INTRODUCTION

Over the last 20 years I have done trigger jobs (on the single action part of the mechanism) on virtually all my firearms. I read everything I could on each gun and the basic theory of trigger operation in order to do it “right”. But it was not until recently when I bought the American Gunsmithing Institutes (AGI) 8 hour Trigger Job course did I really know how to do a trigger job correctly. I have reviewed the DVD’s repeatedly and put to practice the techniques revealed there with great success, at least in my mind. The process makes a whole lot more sense to me now. If you desire to get educated on trigger jobs this article most certainly will get you started. Of course, the best approach is to buy the AGI course (expensive) and do it your self.

I have no affiliation with AGI or gain no profit from this article. I offer it as simply information and education. Do with the information whatever you wish (I am not responsible for your actions). Trigger jobs can impact the safety of your guns. Be aware and be safe!

TERMS DEFINITIONS

The common terms used to describe the process of setting off a firearm and the maladies of the mechanism center around a few words: Pre-travel, Creep, Over-travel.

Pre-travel of the trigger action can also be called trigger take-up and it refers to the trigger travel that does nothing more than take up the “slop” of the pull before anything really starts to happen to set off the gun. European advanced trigger systems always include pre-travel as do most tactical and military firearms. It allows you to pull on the trigger up to the point where serious resistance is just felt without a surprise firing of the gun. It must be low in force to contrast the higher force required to actually set the gun off. Some triggers are designed and or adjusted to not have any pre-travel or at least a minimum amount. The former is called a double stage trigger while the latter is called a single stage trigger.

Creep is the movement of the trigger, after the pre-travel, against the force of the mechanism just before the gun goes off. Creep can be smooth feeling or gritty or notchy or long or some other feel that puts the shooter off in finding the critical spot where the gun goes off. In general creep is considered to be bad but if it exists and you can not feel it, it probably is not really bad. All guns must have some motion of the trigger (creep) to some degree for the mechanism to work. A good trigger has creep that is not distinguishable or noticeable.

Over-travel is the motion of the trigger after the guns goes off. Some shooters like that travel resistance to be long so that the motion of the trigger is not stopped during setting the gun off (these people are in the minority). The rest like to pull through the pre-travel, load the trigger against the mechanism’s force, and have the trigger to apparently never move at all. As stated earlier the mechanism must move some (have creep) and must move beyond the set-off point to assure that the tolerances don’t all build against the mechanism in inclement weather or conditions. A “perfect” trigger feels like there is pre-travel, a force is applied, the gun goes off, and the trigger never moves past the end of the pre-travel. But it is the apparent feel that counts, not the actual motion. Smooth creep and a small amount of over-travel can usually never be felt. It is said that a perfect trigger “breaks like a glass rod”.

PARTS OF THE TRIGGER SYSTEM

The two main types of trigger systems are hammer type and striker type, as used in rifles. Hammer guns can have the hammer exposed as on Colt 1911’s or hidden as in a S&W Model 41 target gun. The hammer is cocked and the trigger action releases it to fly forward into the firing pin (or as in a Colt Single Action Army Revolver the firing pin is attached to the hammer itself). Striker guns have the striker (usually the spring loaded firing pin) held back initially then released by the action of pulling the trigger.

Hammer guns have a spring loaded hammer whose function is to hit (or be) the firing pin, a trigger that transmit the human force into the system, and the sear in the middle that acts as a link between the hammer and the trigger (Colt Single Action Army and similar guns use no sear but have the trigger operate directly on the hammer-the engagement point is often called the sear surface regardless that there is no actual sear part).

Striker guns can have more than one lever that is used as a sear but the function of the sear (or sear surface) is to act to safely retard the action of the firing pin (striker) until a reasonable force is applied to the trigger.

In the systems are springs: a trigger spring to make the trigger return to its initial position, a sear spring to make the sear return to its initial position and to offer a force to keep it engaged, and a hammer/striker spring to give energy to the mechanism that gets transferred to the primer in the cartridge so that the primer will explode to set off the cartridge.

The trigger system includes linkages between the main components that transfer trigger force and a mechanism to safely operate in a single fire mode (a disconnector mechanism that disconnects the trigger from the sear after the hammer/striker is allowed to fall and that allows the trigger to reset with the release of trigger after the gun goes off). Most guns include a way to keep the gun from being fired unless the slide or bolt is completely closed. It is usually in the trigger linkage between the trigger and the sear.

A trigger job modifies the sear engagement surfaces and can include reduced power springs. The idea is to reduce the pull weight (to a safe level), make the trigger feel creep free, and reduce the over travel of the trigger after the gun goes off (optional feature that most users want). The key is modifying the sear surfaces.

THEORY OF SEAR OPERATION

To keep the discussion simple we will describe the trigger operation of a hammer system that includes a normal separate sear actuated by a trigger. It will be easy later to understand how this applies to a system with added linkages, disconnectors, and other variation of the system. This basic discussion is the key to it all.

The hammer includes a notch into which one end of the rotating sear fits. The other end of the sear is touched by the trigger so that force on the trigger rotates the sear which pulls it out of the notch in the hammer. If the hammer notch and the sear end are angled so that the action of moving the sear out of engagement is a straight pull with no motion of the hammer, the engagement is said to be “zero angle”. This sliding of the sear surface on the hammer notch would be on a radial line through the hammer’s center of rotation (the hammer pin).

If the hammer notch and the sear end are angled so that the action of moving the sear out of engagement is NOT a straight pull but results in a movement that is accelerated by the hammer spring, the engagement is said to be “negative angle”. The line of engagement is NOT a radial line but a slope that the sear easily falls off of. In fact it may not be possible for the sear to stay in the notch at all except for the friction between the sear surface and the hammer notch. This is NOT a safe trigger at all! In fact a zero angle trigger is too close to this situation to be safe, as well. Neither of these configurations should be allowed in modifying any trigger system, as they are both unsafe.


If the hammer notch and the sear end are angled so that the action of moving the sear out of engagement is NOT a straight pull but results in a rearward motion (a cam’ing action) of the hammer, the engagement is said to be “positive angle”. Obviously there are degrees of this condition and we should strive to achieve some degree of positive sear angle for safety, but yet the closer to zero the lighter the pull can be. This is because as the hammer is cam’ed back the trigger mechanism has to work against the hammer main spring which in most guns must be substantial in its resistance to get to adequate levels of energy to set off the primer. In a zero angle engagement only the friction of moving the sear across the hammer’s notch is resisting the trigger pull. But remember that the zero angle sear engagement can become dangerous and make the gun unsafe. So we must have positive sear angles.

Ideally both the sear end and the hammer notch should have the same exact angle of engagement to distribute the force of holding the hammer back across the entire engagement surface. This approach allows the wear to be distributed across the entire engagement surface and not on a pointed surface. But typically this is not done and the angles are not equal. If this is the case neither angle, on the end of the sear or in the hammer notch, can be allowed to be anything but positive. If either is negative the engagement as a whole is negative regardless of the other component’s angle. So the engagement must be treated as a whole to gain a safe trigger.

For striker system the notch is in the trigger and the sear rests in the notch. Pulling the trigger allows the sear to slide out of engagement and release the firing pin/striker. Often times there are several levers in the system but only one sear engagement set of surfaces. This engagement must be positive or an unsafe trigger will result.

There are several elements that control the feel of the trigger besides the geometry of the system. The springs (trigger, sear, hammer/striker), the friction between the sear engagement surfaces, the fit and tolerances of the pins that the components rotate on, and friction between moving parts and their housings or the frame of the gun. The spring forces can be reduced to the level that the mechanisms still function perfectly without the extra force. The interferences or friction between moving parts and their housing or the gun’s frame can be looked after. And the sear surfaces can be stoned and polished to reduce the sliding friction. Appropriate lubrication (oil on the rotating parts and moly-disulphide grease on the sear surfaces) can help as well.

One important often-overlooked situation is that any grinding or stoning or polishing of any surface must not remove the hardened surface as applied by the manufacturer. Some parts are made hard throughout but often only the surface, down to a few thousandths, is hardened. Removing that surface reveals soft under metal that will not hold a trigger job for very long. Such radical modification should include renewing the surface hardness or the trigger job will disappear quickly and perhaps the gun might even become unsafe.

THEORY OF THE MODIFIED COLT SYSTEM OF TRIGGER JOBS

Until the cost of labor started to drive the cost of guns upward Colt used a system of sear engagement that gave safe positive sear engagement angles, but reduced the weight of pull as well as the creep. AGI calls a modern adaptation of this system the Modified Colt System. The key is that the engagement is first made positive for safety then the actual sear dis-engagement motion is minimized. The notch depth usually remains the same but the sear is modified with an angle on its inner most surface (about 45 degrees) so that as the sear moves across the notch, the edge of the notch hits the angled inner sear engagement surface and the notch pushes the sear out of engagement. The actual engagement surface can be made small (less than 0.025 inches in most cases, not including the 45 degree sloped surface) but the sear is safe due to the positive angles. The short travel of the sear before the break and the small sear surface itself reduces the creep substantially. The cam’ing of the hammer (from the positive sear engagement angle) does limit how light the pull weight can be but the action of the system is so crisp (remember-breaking glass rod) that the pull weight does not seem as heavy as it actually is. This approach allows perfectly safe 2.5 lb trigger pulls that are creep free and safe on semi-auto center fire pistols but even 4 to 5 lb pulls seem much lighter due to their crispness.


PRACTICAL CONSIDERATIONS

This approach can be used on hammer guns striker guns, rifle, etc.. Some are much harder to implement than others but all guns can be greatly improved with this method. I have successful employed it on several guns. My only concern is all my other guns where I used different approaches that in hindsight might not have been ideal. None of those guns has been a problem but I sure wish I had known this approach earlier.

The one aspect of a trigger job not covered by this system is over-travel. For that the easiest way is to buy an after market trigger that includes a screw that acts as a stop against the back of the trigger guard. Adjust the trigger over-travel screw such that the gun will just not be able to be set off then add some over-travel to assure the gun will fire when hot or cold. Usually about a quarter turn of the adjusting screw gives enough. An alternative is to search out a place on the frame where a screw can be added to stop the travel of the trigger in over-travel. I had to do this on my Browning High Power. Interestingly, I also had to take off the magazine safety (gun could not be fired without the magazine inserted-a poor safety at best) to get the pull at all nice as the safety completely screwed up the trigger action. Be sure to LockTite these screws in place if they are not self locking. On still another gun the firing pin safety (firing pin can not travel unless the trigger mechanism pushes a pin out of the path of the firing pin) spring was way stronger than needed and was greatly affecting the quality of trigger pull. A lighter spring there still did the function but did not interfere with the trigger quality.

If you wish to do trigger jobs on a regular basis or have several guns to do I recommend getting the AGI course. About ten or more common guns are done on the video allowing you to see the pitfalls and to learn how to do it correctly to the finest detail. While the course is a little expensive its cost is less than a visit to the Emergency Room!
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  #10  
Old 06-20-2009, 07:32 AM
LDBennett
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I got the most recent AGI catalog and the #3054 DVD is listed there at $600! I about fell off my chair. This course was under $400 when I paid for it a few of years ago.

The coverage of the course is actually extremely good. But it will be hard to sell at that price! Glad I got mine when I did. I would not have bought it at $600 and think of all the great trigger jobs I have done with the knowledge that would not have gotten done.

Maybe with the above synopsis it will help some of you out there do better and safer trigger jobs. I will no longer recommend the course to the home gunsmith at $600. AGI is out of bed on this pricing. I also note that over the last 12 years their Master Gunsmithing course of study has gone up at least 50%. I love AGI but those pricing levels put them way out of my budget. I can stand a $40 gun specific DVD now and again but the big courses of study are now really out of reach for me.

LDBennett
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  #11  
Old 06-20-2009, 08:55 AM
TheOtherGoose
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Thanks for the information, LD.

I was tempted to post about the new price on the DVD's, but thought it might have sounded argumentative. I agree that $600 is a bit steep for such things, and I wish AGI the best of luck.
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Old 06-22-2009, 05:23 PM
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Heggis Alternatives?

I'm a new Buckmark Target Contour Lite owner (finally "graduated" from a Ruger Mk II) and have read most of hundreds of posts in the BM trigger-tuning thread. I've tried the Heggis flip, and yes, things got better. However, while taking NO side in the on-going pro/anti flip debate, I would appreciate a review (or directed reference) of BM trigger-tuning suggestions that allow the sear spring to stay in the factory orientation. The truth is, post flip, my sear spring legs seemed ill-positioned. In an attempt to match the posted photos I inadvertantly broke (shortened) one of the legs. I now want to buy a new sear spring, put it in the factory position, install an over-travel screw in my trigger (or buy a Silhoutte trigger) & try to tune my BM. What's the process? (or who's the best 'smith to hire it done?) Thanks!
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