I seldom contribute, but often read and learn from this forum. I thought this (the Brno 21/22 Double Set Trigger) might be a worth while topic for a post. I am not sure if this post should in the "gunsmithing" section, but given that I am not one, I felt it should probably go here in close proximity to the other Brno 21/22 posts. Also, By being here in the sporting section it will also likely receive more traffic and maybe those that really do know what they are doing can critique my post. I suspect the moderators will adjust accordingly.
I am a fan of Brno 21/22 rifles; I have had a few as well as a ZG-47. I think they are extremely well made, but I will be the first to admit that (the often compared CRF) the FN Winchester Model 70 functions smoother and are generally more user friendly. That being said, one (the Model 70) is more like a nice new pickup truck and other is more like a classic British sports car (Brno 21/22). There are goofy little things about the 21/22 rifles that irritating (i.e. safety, floor plate, etc.) but when shouldered and swung they just feel great (inexplicably nice in the hands); where as a new Model 70 is just fine, but just feels pedestrian in comparison.
However, this is not a post comparing the FN Model 70 to the Brno 21/22. This is a post about rectifying one of those irritating things about Brno 21/22; the double set trigger. I have a had two with double set triggers and one with a single trigger. One of my double set trigger (DST) models (a Brno 21H) was perfect; 4(ish) lbs primary and 1(ish) lbs set. My second (a Brno 22H) that I recently acquired from member on here had a horrendously heavy primary (unset) trigger pull (must have been over 10 lbs) and set trigger that would go off in a strong wind. In general, I am a fan of one good trigger over two, but I knew that the primary trigger could be made to work as a totally acceptable trigger and that it was possible to have a heavier set trigger so I set out to achieve that with the new 22H.
Caveat: Not a gunsmith, not a gun expert, or even very mechanically inclined so take what I say with a grain of salt.
I did the typical Google research for fixing poor DST pull weights, but all I got was:
My first mission was to fix the primary trigger. There are two springs working on the primary trigger one is a little flat spring in the front of the trigger group that serves to keep forward tension on both a part of the set trigger system and the main trigger and the other is the sear spring (as most of you will recognize, the DST sear system is really fairly similar to regular military Mauser with a sear bar that pivots around a pin with the sear at the rear and the sear spring on the other). You may also consider the main firing pin spring as a contributing spring force source for the primary trigger as it controls the pressure between the cocking piece and the sear, but I felt like that would not be my first choice if I was going to start tinkering. Also, my Google research informed me that [on a regular military Mauser trigger] approximately 70% of the trigger weight is the main sear spring and 30% is the weight of firing pin spring (I think the fire pin spring is greater contributing factor then what I read, but obviously it depends on a variety of conditions including the condition mating surfaces of the sear and cocking piece. So this is what I did:
1. Take a part the sear bar system and the DST system one piece at a time and clean the 73 years of dirt and grease. The Princess Auto brass punch set is very helpful. Take pictures before removing pieces.
2. Replace everything and test pull the weight. The primary trigger is still very heavy.
3. Replace the main spring. I knew that it is common trick to use the floor plate latch spring as the sear spring which I didn't want to do, but it did tell me that I can change weigh with a different spring and of course Google provided lots of examples of people trying this some with great success and others that failed or made things worse. I put a ball point pen spring in place of the sear spring to test what would happen. It did lighten the trigger, but it was a poor fit and the sear won't return full into place.
4. Go to Canadian Tire a pick out two of the same spring with similar dimensions but a little longer than the original sear spring. The main spring is very heavy duty and quite stiff. The new springs were similar in weight, but just a little lighter duty. So I cut the new spring to an length four or five coils longer than the original to attempt to replicate a similar compression weight to the original then proceeded with the following process: install, test, make a qualitative notes about the performance (I don't have a trigger pull weight gauge), remove, clip the spring, and repeat until I had got too short to work properly.
5. Select what I thought was best weight to sear engagement (about 2 coils longer than the original) and clip the other new spring to that length.
6. Install the new spring and test the hell out of it to check for the potential for a slam fire, accidental discharge, poor sear engagement, or changes to the performance in the set trigger.
7. Success, the new trigger is probably 5lbs (ish), pretty crisp, and seems to function very well. I put my notes and the original sear in a labelled baggie and stuck them in the parts bin.
My second mission; adjusting the set trigger weight. The trigger pieces are pinned in place in the bottom metal and located in the middle of a large flat spring that is held in place by a large blued screw at the front of trigger group. Setting the set trigger results in the lifting and "loading" of the big flat spring which can cause the initial setting of the set trigger to actually require a fair bit of force. Once the set is pulled you loaded the force of the big spring on a mini sear piece that is released by the pull of the primary trigger. The force required to release the seems to be controlled in part by the little flat spring and the mating surfaces of the mini sear. Once the set primary trigger is pulled (or breathed on), the force of the big flat spring powers (really hard and fast) the connection between the DST system and the sear bar system. I didn't know where or how I could source a replacement for the little flat spring and I didn't want to start buggering with the physical shape of the sear so I decide my mission would be to adjust (ever so slightly) the angles of mating surfaces between the primary trigger and the little spring and the mini sear via the little screw between the triggers and the big blued screw. This was all fairly intimating because of how fine the surfaces were and minuet forces required to make the system work. So this is what I did:
1. Adjust the center screw (between the triggers) in and out to find the "heaviest" weight I could while still having the set work. If you screwed the screw in too far the set won't catch the mini sear when engaged.
2. I started adjusting the big blued screw holding the big flat bar in place. I discovered there was room to screw this in tighter (and looser). Tightening the screw increased the load on the big flat spring and changed the position of the little flat spring. Loosening had a similar effect but once loosened too far the little flat spring could move side to side and change it's connection to the rest of the trigger system. It was challenging to put in back in the correct position, but after some swearing and sweating, I had the big flat spring, the little flat spring, and the big blued screw back in the correct position (take lots of pictures). What I learned was that slightest changes in the little flat spring and big flat spring does change that weight and creep of set primary trigger.
3. Using the tiniest adjustments on the big blue screw between "pretty tight " (like my 2 year old wouldn't have the strength to move the screw) and really tight I search for the best pull. I would move the screw in "one hour" (like if the screw was the hour hand on a clock) adjustments from "really tight" to as a loose as I was comfortable with and tested the pull of the set primary trigger. There was a small but noticeable change in pull weight and feel ("creep", but not really creep because it is so light) over the test and eventually I came to rest on spot I thought was usable.
4. Then I tested the hell out of it and used the my reloading calipers to test for lateral movement in the position of flat bars.
The end result of approximately 6 hours of an untrained monkey doing trial and error testing on the Brno 22H DST system was that the primary unset trigger went from 10+lbs to about 5 lbs and the set trigger which went from silly light weight to "at least I can settle my finger on the trigger" weight (pull weight is still ounces not pounds). Obviously, there was some engineering that went into the original trigger system and there may be a reason that main sear spring was so heavy (maybe reliability?), but I have my load development to do for the Brno 22H so I will have lots of time and shooting to allow for testing and monitoring. I will update if I run into any issues.
Here are a few pictures to help with the story:
I am a fan of Brno 21/22 rifles; I have had a few as well as a ZG-47. I think they are extremely well made, but I will be the first to admit that (the often compared CRF) the FN Winchester Model 70 functions smoother and are generally more user friendly. That being said, one (the Model 70) is more like a nice new pickup truck and other is more like a classic British sports car (Brno 21/22). There are goofy little things about the 21/22 rifles that irritating (i.e. safety, floor plate, etc.) but when shouldered and swung they just feel great (inexplicably nice in the hands); where as a new Model 70 is just fine, but just feels pedestrian in comparison.
However, this is not a post comparing the FN Model 70 to the Brno 21/22. This is a post about rectifying one of those irritating things about Brno 21/22; the double set trigger. I have a had two with double set triggers and one with a single trigger. One of my double set trigger (DST) models (a Brno 21H) was perfect; 4(ish) lbs primary and 1(ish) lbs set. My second (a Brno 22H) that I recently acquired from member on here had a horrendously heavy primary (unset) trigger pull (must have been over 10 lbs) and set trigger that would go off in a strong wind. In general, I am a fan of one good trigger over two, but I knew that the primary trigger could be made to work as a totally acceptable trigger and that it was possible to have a heavier set trigger so I set out to achieve that with the new 22H.
Caveat: Not a gunsmith, not a gun expert, or even very mechanically inclined so take what I say with a grain of salt.
I did the typical Google research for fixing poor DST pull weights, but all I got was:
- "adjust the screw in between the triggers" - This very mildly changed the weight of the set trigger and change the take-up on the primary trigger.
- "the parts are worn, you can't fix them" - This didn't seem likely based on the materials, the condition of the gun, and the potential parts that could be worn.
My first mission was to fix the primary trigger. There are two springs working on the primary trigger one is a little flat spring in the front of the trigger group that serves to keep forward tension on both a part of the set trigger system and the main trigger and the other is the sear spring (as most of you will recognize, the DST sear system is really fairly similar to regular military Mauser with a sear bar that pivots around a pin with the sear at the rear and the sear spring on the other). You may also consider the main firing pin spring as a contributing spring force source for the primary trigger as it controls the pressure between the cocking piece and the sear, but I felt like that would not be my first choice if I was going to start tinkering. Also, my Google research informed me that [on a regular military Mauser trigger] approximately 70% of the trigger weight is the main sear spring and 30% is the weight of firing pin spring (I think the fire pin spring is greater contributing factor then what I read, but obviously it depends on a variety of conditions including the condition mating surfaces of the sear and cocking piece. So this is what I did:
1. Take a part the sear bar system and the DST system one piece at a time and clean the 73 years of dirt and grease. The Princess Auto brass punch set is very helpful. Take pictures before removing pieces.
2. Replace everything and test pull the weight. The primary trigger is still very heavy.
3. Replace the main spring. I knew that it is common trick to use the floor plate latch spring as the sear spring which I didn't want to do, but it did tell me that I can change weigh with a different spring and of course Google provided lots of examples of people trying this some with great success and others that failed or made things worse. I put a ball point pen spring in place of the sear spring to test what would happen. It did lighten the trigger, but it was a poor fit and the sear won't return full into place.
4. Go to Canadian Tire a pick out two of the same spring with similar dimensions but a little longer than the original sear spring. The main spring is very heavy duty and quite stiff. The new springs were similar in weight, but just a little lighter duty. So I cut the new spring to an length four or five coils longer than the original to attempt to replicate a similar compression weight to the original then proceeded with the following process: install, test, make a qualitative notes about the performance (I don't have a trigger pull weight gauge), remove, clip the spring, and repeat until I had got too short to work properly.
5. Select what I thought was best weight to sear engagement (about 2 coils longer than the original) and clip the other new spring to that length.
6. Install the new spring and test the hell out of it to check for the potential for a slam fire, accidental discharge, poor sear engagement, or changes to the performance in the set trigger.
7. Success, the new trigger is probably 5lbs (ish), pretty crisp, and seems to function very well. I put my notes and the original sear in a labelled baggie and stuck them in the parts bin.
My second mission; adjusting the set trigger weight. The trigger pieces are pinned in place in the bottom metal and located in the middle of a large flat spring that is held in place by a large blued screw at the front of trigger group. Setting the set trigger results in the lifting and "loading" of the big flat spring which can cause the initial setting of the set trigger to actually require a fair bit of force. Once the set is pulled you loaded the force of the big spring on a mini sear piece that is released by the pull of the primary trigger. The force required to release the seems to be controlled in part by the little flat spring and the mating surfaces of the mini sear. Once the set primary trigger is pulled (or breathed on), the force of the big flat spring powers (really hard and fast) the connection between the DST system and the sear bar system. I didn't know where or how I could source a replacement for the little flat spring and I didn't want to start buggering with the physical shape of the sear so I decide my mission would be to adjust (ever so slightly) the angles of mating surfaces between the primary trigger and the little spring and the mini sear via the little screw between the triggers and the big blued screw. This was all fairly intimating because of how fine the surfaces were and minuet forces required to make the system work. So this is what I did:
1. Adjust the center screw (between the triggers) in and out to find the "heaviest" weight I could while still having the set work. If you screwed the screw in too far the set won't catch the mini sear when engaged.
2. I started adjusting the big blued screw holding the big flat bar in place. I discovered there was room to screw this in tighter (and looser). Tightening the screw increased the load on the big flat spring and changed the position of the little flat spring. Loosening had a similar effect but once loosened too far the little flat spring could move side to side and change it's connection to the rest of the trigger system. It was challenging to put in back in the correct position, but after some swearing and sweating, I had the big flat spring, the little flat spring, and the big blued screw back in the correct position (take lots of pictures). What I learned was that slightest changes in the little flat spring and big flat spring does change that weight and creep of set primary trigger.
3. Using the tiniest adjustments on the big blue screw between "pretty tight " (like my 2 year old wouldn't have the strength to move the screw) and really tight I search for the best pull. I would move the screw in "one hour" (like if the screw was the hour hand on a clock) adjustments from "really tight" to as a loose as I was comfortable with and tested the pull of the set primary trigger. There was a small but noticeable change in pull weight and feel ("creep", but not really creep because it is so light) over the test and eventually I came to rest on spot I thought was usable.
4. Then I tested the hell out of it and used the my reloading calipers to test for lateral movement in the position of flat bars.
The end result of approximately 6 hours of an untrained monkey doing trial and error testing on the Brno 22H DST system was that the primary unset trigger went from 10+lbs to about 5 lbs and the set trigger which went from silly light weight to "at least I can settle my finger on the trigger" weight (pull weight is still ounces not pounds). Obviously, there was some engineering that went into the original trigger system and there may be a reason that main sear spring was so heavy (maybe reliability?), but I have my load development to do for the Brno 22H so I will have lots of time and shooting to allow for testing and monitoring. I will update if I run into any issues.
Here are a few pictures to help with the story:
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