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Discussion Starter · #1 · (Edited)
Reading jonpo's thread about yugo part features ( http://www.theakforum.net/forums/30...planations-yugo-part-differences-updated.html ) I found the interesting fact that M64's had a bolt hold open after last shot feature, and seems to be the kind of BHO that mantains the bolt open after magazine is removed.

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I was wondering if this feature could be adapted in some way to other models.
I supose this works with a spring loaded internal lever, but I would be grateful if someone that owns an M64 uploaded some captures of the mechanism.

Thanks in advance.
 

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Discussion Starter · #2 ·
Well, I finally found the photos by my own means.
I'm going to try to adapt the design to an M76 reciever. Hopefully I'll be able to make a design that works wihout more modification than a small cut in the reciever internal rail (an affordable modification for anyone who has a dremel, or a file and much patience).

I'll start working on it as soon as I return home for chrismas.


Photos from ar15.com ( Why does the AK have no bolt hold open? - AR15.Com Archive )


 

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If you can make one that works reliably, I'd be happy to buy one for one of my M64s. Keep in mind that it requires a notch in the magazine so the floor plate can push up the lever.
 

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Discussion Starter · #4 · (Edited)
If you can make one that works reliably, I'd be happy to buy one for one of my M64s. Keep in mind that it requires a notch in the magazine so the floor plate can push up the lever.
Since wmy rifle is an M76, the dimensions and probably even shape will be different (I'll try to make it modifying as less as possible the reciver).
If the prototype works correctly and there's enough people interested I'll contact a gunsmith to make a bunch of them with better quality and finnish.

That done I could try to make a version for both milled and stamped reciever AK's, but there's another problem with that:
7,62x39 is banned for semiautos in Spain, because of being a "military round". Because of that, AK's are extremely rare, and absolutely overpriced (about 1200€). And to avoid ban, they must have the gas piston cut out and the gas port blocked.
It will be nearly impossible to get an AK to test the piece, so I would need exact diagram of the reciever in order to make it.


Is it an original M64 milled reciever? if it is it would be much easier since I just need the measurements to copy the original part. But in that case, if I was you, I would show my previous post photos to a gunsmith and get all the job done by him, since he'll have the rifle to check correct funtionality.

Of course I keep on mind I'll need to dremel a notch in the magazine, but that's the easiest part of all.
 

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Discussion Starter · #5 · (Edited)
Well, here is my first sketch for the BHO.

It attaches to the hammer pin (2). (1) marks the bolt head, and (3) the piece that's pushed up by the magazine follower.
I've done this without having the gun in front of me, so it's just the essential idea. I'll have to figure out how to make a stop, to prevent the piece from rotating down into the reciever (the spring would fall out of it's place).



I basically took the original M64 design and reversed the rotation point.
This should work on any AK. Obviously dremeling out a small portion of the reciever rail, and cutting a notch on magazines will be necessary. Also AK piece will differ in lenght from M76 piece.


The original piece:



 

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There are some good pictures in the Grim Reaper about these BHO levers. There was also a thread about 3-4 years ago where a member posed pictures of an original piece. Unfortunately, I have never seen a real one. I'd pay handsomely for an original...
 

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The problem with the design is that you still have to manipulate the charging handle, even if it's just slightly, which pretty much negates the advantage of a bho device. I want one because it's cool; not really because it's useful.
 

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Discussion Starter · #9 ·
There are some good pictures in the Grim Reaper about these BHO levers. There was also a thread about 3-4 years ago where a member posed pictures of an original piece. Unfortunately, I have never seen a real one. I'd pay handsomely for an original...
Thank you, that's a big help.
I'll have to check if that design really doesn't need a cut in the rail. The bad thing is if it doesn't need it, I will most probably need a a new hole in the reciever. And that's much more complicated.
In adition, that piece seems surdy enough for an AK, but I doubt it will resist the M76 heavy bolt impact for much time.
 

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Discussion Starter · #10 ·
The problem with the design is that you still have to manipulate the charging handle, even if it's just slightly, which pretty much negates the advantage of a bho device. I want one because it's cool; not really because it's useful.
I must disagree. VZ58 doesn't have a mag release button, but the reloading speed and simplicity makes a big difference, when compared to the magazine blocking the bolt as happens in the M76. Much more when compared to a normal AK, in which you can easily go to the point when you need to fire and -surpise- there's no round in the chamber.

Anyway, It would be awesome to have a mag release button, but I just can't see the way without having to perform heavy modifications to the reciever. I'll look for a way wen I have the gun to check, but most probably I won't find one.
 

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Discussion Starter · #11 ·
After doing some research and thinking I've come to the conclusion that it's impossible to make an inversed lever type bolt hold open. The reason is that if an angle exists between bolt trajectory and BHO rotation point, the bolt will allways force the BHO back down (stupid me).

Also thought that the simplest desing for a bolt release button would be at the side of the magwell, and it would require a small notch for it to come out.

Having this factor on mind, there are just three options for BHO designs:

a) M64 type BHO, that would require drilling the reciever. Bolt release button would be possible.
b) Linear, vertical type BHO, as in the VZ58 or the PSL, no gunsmithing needed, but it would need to be made out from two pieces, and would be more likely to end up breaking. Bolt realease button would be simple to make for this design, but would require dremeling a notch in a side of the magwell.
c) Hooked, inversed angular BHO. Drop in. Would have a protruding ending to prevent it from being pushed down by the bolt, by getting hooked to the hollow part where the round sits. No bolt release button.
 

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Discussion Starter · #12 ·
I think option B) is the way to go. I have a couple of designs that seem sturdy enough, and I see no reason why they wouldn't work.
The only con is machining complexity. This pieces are over my skills, I don't think I could make a decent prototype by my own means. And it will be more expensive than the original.
 

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I like the Vepr12 design the best. Never liked the Yugo method as when you remove the mag the bolt goes forward.
 

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I like the Vepr12 design the best. Never liked the Yugo method as when you remove the mag the bolt goes forward.
That is the Yugo magazine BHO. The Yugo mechanism BHO discussed and pictured here is different. Bolt release via pulling charging handle to the rear releases bolt & carrier.
 

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Discussion Starter · #15 ·
I took measurements from the M76 reciever. I allready have a final two-piece design, just need to make it more precise. Then I'll make a 3D model for CNC production (beggining a prototype to check functionallity and modify tolerances if needed).
One of the problems with the (original) M76 is that the disconnector leaves a really small space for the BHO. Adapting it to a semiauto AK will probably be much easier.

I would like to ask you for some photos of semi-auto AK recievers (stamped and milled) to get a better idea of the modifications that I'll need to perform on the original design. Then I'll have to find someone with an AK (really rare in my country) to take measurements and function-check.
 

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Very interesting topic. I was thinking of experimenting with my own design before coming across this post. Any new developments?

Are you allowed to have one of the Polish 80% blank AKM receivers? You might be able to glean some info from one of those. If so, I'll send you one.
 
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