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-   -   Put an 7-2 in an 7-4 stock (trigger mod) (https://www.rimfirecentral.com/forums/showthread.php?t=1168335)

hara-julu 08-05-2019 12:28 PM

Put an 7-2 in an 7-4 stock (trigger mod)
 
I have done two of these now and something like a process is forming, will share. I am a tinkerer, not a machinist, engineer or smith. The mechanics of these 7-2 triggers are pretty simple, but all caveats apply, if you are in any way not comfortable with firearms modification, read for entertainment only.

So the 7-2 is an really fun rifle, the paddle action is the defining feature, nice trigger is next (imho) and the bull barrel with recessed crown is third. The small birch stock however is not in the same class as the hardware it holds.

Thankfully its big sister the 7-4 has a strong following in the biathlon community, which is where I crossed paths with my first 7-2. Stocks for an 7-4 are plentiful and varied and more importantly available for purchase. Unless you are one of the supremely talented folk making stocks on this site, you are out of luck.

The bear stock is one of my favorites (and what I run), a bit expensive and there are many options: Lost Nation, Larsen, Biatar...

https://hosting.photobucket.com/imag...080&fit=bounds

So the reason one can not simply get a 7-4 stock and jam in an 7-2 action is trigger placement. THe trigger on an 7-2 is extended from the rear of the trigger assmbly and will want to be approximately where your neat new palmswell is occupying on that new stock. No joy.

Here is an 7-2 action, not the trigger coming from the rear of the trigger assmbly

https://hosting.photobucket.com/imag...080&fit=bounds

Fortunately, all the other measurements are the same between the 7-2 and 7-4. Mounting lug locations? yes, contact points, yes. Magazine location? yes. Paddle clearance? yes. Just the trigger location (and safety) are different (and dry fire mechanism, more later)

Here is a picture with the mag well lined up of the trigger guard from an 7-2 below against an 7-4 stock with an modified trigger (my first attempt)

https://hosting.photobucket.com/imag...080&fit=bounds

So the trigger needs to extend directly south of the trigger block. THe trigger is a simple lever with a pivot point, drift out the pin and have a look:

https://hosting.photobucket.com/imag...080&fit=bounds

So a cut here and a grind later the trigger is now a stub. It is important to leave the rear segment for about 1/4" as this will impact the rear of the trigger frame as an over-travel control.

https://hosting.photobucket.com/imag...080&fit=bounds

You can see an trigger I ground up from an 170 year old iron nail, surplus from an ongoing remodel.

The trigger is fit pretty snug and devcon does the rest. I am careful to leave a little extra devcon on the bottom to "build" some additional lateral support. An real machinist could use threading or alternate mechanical approach but I warn the trigger is of unknown material, feels like an steel something alloy, pretty light and I fear would melt away under any real heat.

https://hosting.photobucket.com/imag...080&fit=bounds

A simple rig to hold everything square during gluing goes a long way.

So from here it is reassembly (and a few turns on the trigger spring adjustment to get the pull nice and light) and we can see the trigger is now oriented correctly.

https://hosting.photobucket.com/imag...080&fit=bounds

Oh, right, grind of the extra!

https://hosting.photobucket.com/imag...080&fit=bounds

And drop it in the fancy new larsen stock:

https://hosting.photobucket.com/imag...080&fit=bounds

Go race!

(If you are in new england, we race at HSC Biathlon in Harvard MA, pm me and come on out)

Gobber 08-05-2019 08:21 PM

That is so cool! I have read that people have reworked their triggers, but a picture is worth 1k words. It is really nice to move the trigger face further forward for grip placement. Projects - give me more projects! :eek:

Triggershoe 08-06-2019 07:30 AM

hara-julu: To do this mod, it appears that you lose the safety mechanism entirely? Is that an issue anywhere you "race" or otherwise? Also, the trigger bar/lever, did you also make that from scratch, or is that the factory piece simply cut down?

hara-julu 08-06-2019 10:32 AM

TS

The trigger bar was re-used, just the trigger end was removed. The last time I did this it was completely fabricated, but that isn't needed. There is more than enough material to support the blade type trigger I used.

Biathlon rifles don't require a manual safety (and I have not encountered an 7-4 retaining the "paddle" type safety, these are hard to activate wearing gloves).

The next time I do this there will be two holes for a horizontal bar to attach (using an u shaped bar stock welded into the two holes, which will allow for competition triggers and provide fore/aft and up down adjustability)

Triggershoe 08-06-2019 12:58 PM

Quote:

Originally Posted by hara-julu (Post 11566417)
TS

The trigger bar was re-used, just the trigger end was removed. The last time I did this it was completely fabricated, but that isn't needed. There is more than enough material to support the blade type trigger I used.

Biathlon rifles don't require a manual safety (and I have not encountered an 7-4 retaining the "paddle" type safety, these are hard to activate wearing gloves).

The next time I do this there will be two holes for a horizontal bar to attach (using an u shaped bar stock welded into the two holes, which will allow for competition triggers and provide fore/aft and up down adjustability)




hara--That makes sense about the safety.. the rifles are only loaded and shot at specified intervals/locations, so no real need for a safety. It's not like you are carrying the rifle around fully loaded with a round chambered. As far as your idea about fore/aft adjustability of the trigger shoe, can you post a drawing of how that would be done/look like using the 7-2's trigger mechanism? I would like to do such a mod to my "regular" 7-2. I find I have to "reach" for the trigger more than I like, and would like to be able to move the shoe rearward a bit. I assume this (my reaching for the trigger) is more due to the 7-2's stock design than anything else. Unfortunately, the pistol grip area just places my hand such that it feels slightly awkward for my index finger to reach the trigger. At least for ME it does....

As an aside, I noticed the serial# on your rifle ---2091), mine is 2095! Probably both of our rifles made within minutes of each other, certainly within hours.

hara-julu 08-07-2019 08:11 AM

1 Attachment(s)
TS

Yes, we seem to have matching 7-2's. I enjoy looking at the tooling marks on these and thinking about what the machining line must look like. There is some old school metal work going on in that plant.

Here is what I was thinking about for the adjustable trigger block. Let me add more caution, I would not use this without a lot of testing. With the simple modification I did above, the trigger functions well. I have over a year on the first iteration without issues. The leverage point is changing and that is changing the perceived pull. The simple modification I made is nice for a light trigger. The rail approach I copy here is used on the 7-4 and also the Annies. Again, this is only illustrative.

Triggershoe 08-08-2019 07:41 AM

Quote:

Originally Posted by hara-julu (Post 11567269)
TS

Yes, we seem to have matching 7-2's. I enjoy looking at the tooling marks on these and thinking about what the machining line must look like. There is some old school metal work going on in that plant.

Here is what I was thinking about for the adjustable trigger block. Let me add more caution, I would not use this without a lot of testing. With the simple modification I did above, the trigger functions well. I have over a year on the first iteration without issues. The leverage point is changing and that is changing the perceived pull. The simple modification I made is nice for a light trigger. The rail approach I copy here is used on the 7-4 and also the Annies. Again, this is only illustrative.

H-J: Old school indeed! But I guess they got it "right" where it needs to be. One thing that cracks me up is that massive extractor claw on the bolt and bear-trap strength spring associated with it. You are simply NOT going to "stick" a loaded round in the chamber of these rifles, it IS coming out when you pull on that toggle! Regarding the trigger, I get the idea (the adjustable rail thing) from your picture. Also, I noted the change in the trigger's leverage point as soon as I saw your trigger modification in your previous posts. That is a huge change in that regard. I gather that the trigger movement required (total trigger movement 1st and 2nd stage combined) to fire the gun is greatly reduced with your "new" trigger blade placement?

hara-julu 08-08-2019 09:28 AM

TS,

Yes, pull came down to about 18 oz, then a 1x turn on the spring retainer got to 14 oz. The far rear trigger (stock configuration) is misleading in leverage since it introduces rearward pull which works against the downward action that releases the sear. Pulling the stock trigger is almost like lifting the trigger. The new location makes it a pure pivot action on the pin. The "floor" reliable pull weight is around 6 oz, which is way too light for my comfort, I can trip it with a popsicle stick held at the end between two fingers. I did zero mod to the sear, trigger/sear engagement surface, like you said, the designer got it right where it counts on this rifle. Tight chamber, massive extractor to match the tight chamber, recessed crown to avoid me messing it up when the rifle becomes a blunt instrument (falling on xs skis).

One hidden attribute of the action is that the extraction port is huge, making our relay round feeding (spare rounds fed by hand) possible without taking off the gloves. The PWS Summit action did not make this easy and that was one reason it didn't translate to the biathlon crowd.

-HJ

Triggershoe 08-08-2019 04:40 PM

Quote:

Originally Posted by hara-julu (Post 11568213)
TS,

Yes, pull came down to about 18 oz, then a 1x turn on the spring retainer got to 14 oz. The far rear trigger (stock configuration) is misleading in leverage since it introduces rearward pull which works against the downward action that releases the sear. Pulling the stock trigger is almost like lifting the trigger. The new location makes it a pure pivot action on the pin. The "floor" reliable pull weight is around 6 oz, which is way too light for my comfort, I can trip it with a popsicle stick held at the end between two fingers. I did zero mod to the sear, trigger/sear engagement surface, like you said, the designer got it right where it counts on this rifle. Tight chamber, massive extractor to match the tight chamber, recessed crown to avoid me messing it up when the rifle becomes a blunt instrument (falling on xs skis).

One hidden attribute of the action is that the extraction port is huge, making our relay round feeding (spare rounds fed by hand) possible without taking off the gloves. The PWS Summit action did not make this easy and that was one reason it didn't translate to the biathlon crowd.

-HJ

HJ- The stock 7-2 trigger pull feels almost awkward to me. My hand position on the pistol grip of the stock is contributory toward that feeling. It always feels as if I'm "reaching" for the trigger. That, combined with the stock trigger's "back and upward/lifting" pull arc doesn't help either. Fortunately, I'm still able to shoot the rifle well due to the very light and crisp break of the trigger. I've lightened mine substantially and also tweaked the sear engagement a TINY bit to eliminate a small amount of "creep" present in the 2nd stage. The actual "break" of the trigger is really very nice.

midwest swiss 08-11-2019 02:40 PM

This is the best tinker deal for the 7-2 that
I have seen on rfc in a long time.
My 7-2 likes to shoot flyers horizontal and I
have norowed it down too the trigger doing
this. My brain is thinking now because of this thread.
I would like too make a new trigger piece instead of cutting up the OEM trigger and
I have too have a safety. Good winter project.

Midwest Swiss

hara-julu 09-05-2019 08:30 AM

So I had my 7-4 action out of the stock for cleaning and thought it would be a good compare versus the 7-2 pictures earlier in the thread.

This showd the trigger attach on an "rail"
https://imgur.com/6EUGyMI

hara-julu 09-05-2019 08:31 AM

Another try with an different link (new host)
url=https://imgur.com/6EUGyMI]http://i.imgur.com/6EUGyMI.jpg[/url]

hara-julu 09-05-2019 08:51 AM

Here you can see the three adjustments available
(a) first from left is over-travel, which adjusts how far the trigger travels after releasing the hammer,
(b) the middle adjustment is for sear engagement and adjusts how close to the edge your sear is which controls length of pull at pressure (second stage) as well as pull weight (which is an complex product of stage one and stage two weight)
(c) the stage one is the right most, and is tightening/loosening the spring which controls how much pressure is needed to reach stage two.

The over-travel is "to taste" adjust as you like, the second stage is a matter of fire control safety, it is very important to have right or you may face bang/bump/slam fires. If you don't know what those are, don't touch the middle adjustment. The first stage pressure is what keeps the trigger from inadvertently reaching a second stage pull as you are handling the rifle, target/competition weight and sporting weight is different and sometimes mandated.

https://i.imgur.com/2TKWtV6.jpg

hara-julu 09-05-2019 09:02 AM

Here are a bunch more looks at the trigger assembly

This is an "dry file" hammer control which interdicts the hammer when there is no magazine inserted.
https://i.imgur.com/s78EUbL.jpg

Another look at the dry fire control:
https://i.imgur.com/byK9fGz.jpg

This could probably be copied and retrofit to an 7-2 trigger assembly:
https://i.imgur.com/HOSpYFi.jpg

https://i.imgur.com/N66dqKr.jpg

This shows the sear/hammer engagement:
(you don't want this too shallow, not all sear edges are perfectly parallel to the hammer surface, and the release becomes "spooky" as stage two gets lighter.
https://i.imgur.com/MxDPlFI.jpg

Triggershoe 09-06-2019 07:22 AM

HJ---Thanks for those great pics of the trigger assy. In your post #14... the LAST pic specifically: what do the parts necessary to accomplish the fully ADJUSTABLE PULL WEIGHT on the 7-4 look like? Could these parts possibly be retrofitted to a 7-2 trigger? I would guess the 7-2's safety mechanism would interfere, and make this mod a no-go. I can just see a bit of the part that attaches to the lower end of the spring. This must be some type of threaded "block" that the adjustment screw threads into, to basically shorten or lengthen the trigger pull spring. Very curious how this all works and looks internally. If you have had this trigger apart, do you have any pics of these particular parts?


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