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scratch build 7.62x25 on ak reciver blow back

17K views 165 replies 15 participants last post by  1biggun 
#1 · (Edited)
Xxxx
 
#7 ·
It seems the point of his build as mentioned is to do it a simple and basic with a minimum of tools as possable. I also think it needs to have a extractor and im still not sure how the ejection angle is controled. Pretty cool though thanks a ton for the link
It has no extractor, it is straight recoil, so it doesn't really need one, it has no topcover, so the angle doesn't matter so much, as any direction pretty much is out.

Here's a link to the "condensed" version I posted in your other thread.
24HR-AK47

EDIT: :rofl: On page 102/103 he almost makes it into an open bolt submachinegun without knowing.
 
#11 ·
How about something along this line:

ordinary AK receiver and rails

custom front trunnion with hole for guide rod.

custom bolt - you could saw the slots in the sides, or mill steps in a second piece and bolt or weld it together

AK firing pin, extractor

press barrel in so it lines up with the magazine feed lips, as needed


In my sketches of a "mostly homebuilt blowback AK" I always run into trouble with the top cover, RSB, GB, and handguard bits. The AK stuff is complex since Kalashnikov wanted everything to come off without tools for cleaning; if you can simplify things it would be easier to build.
 
#14 ·
Im staring at a striped bolt and extractor from a AK an d thinking the factory style is doable. IM not real fermilular with the AR stuff I have a couple striped lowers and perhaps now is the time to order some of the parts for my ARs so I can study them.
The AR firing pin has a rear travel stop that is just a huge ring near the end, you just put a pin across it and the pin goes nowhere. With the AK the pin has to be located pretty precisely.

Here, I'll get a link to a pic of an AR firing pin to show what I'm talking about, in case you haven't seen one. http://sttgl.com/30060901/page graphics/inv/AR15 firing pin.jpg
 
#16 ·
That is pretty much what the AK extractor needs, only without the slot. Wish I had thought of using AK parts back when I made my bolt, ended up milling like an eighth of the weight off to throw a AR extractor on it, now my bolt is probably too light.
 
#17 ·
What about a pistolextraktor? It only need a slot you can make with a hacksaw and two holes drilled one for a pin and one slightly bigger for a spring.
any links?

Here, I'll get a link to a pic of an AR firing pin to show what I'm talking about, in case you haven't seen one. http://sttgl.com/30060901/page gra...ring pin.jpg

Thanks for the link knowing whats out there and what it looks like is half the battel. so what exactly are firing pins mad of how ard are they?? will drill rod that benn hardend work. I like how the ar has a bulge in it to but a spring in front of. I want a spring loaded firing pin I think. How hard are the factory primers??

for the carrier assembly im thinking of possably a carrer made from normal steel with a hole drilled through it that a bolt possabply a choulder bolt like mentioned before could bb inserted into and either pinned in place or have a nut on the back. then it can be changed or even shimmed to agjust head space ect. Im thinking square block with two holes one for the recoil spring to go into and one for the bolt to insert into aand some slots on the sides milled to fit through the mag lips. and to jit the hammer correctly and all that. I got to get some ammo a reamer and some barrel blanks fist. although I could do a 9mm with what I have on hand to get the bugs worked out and figure what will work.
 
#18 ·
You will need a spring loaded firing pin if you use a standard ar15 firing pin. I just use a spring thats fairly close to a suomi sear spring when I convert a suomi bolt to semi. Since the bolt stops suddenly a lighter spring (or no spring) can allow the firing pin to move foreward enough to set off the chambered round. I tested several springs and ended up going with a heavy .028" diameter wire spring which kept the firing pin from leaving much except a slight mark on the winchester and remington sp primers I used. Since you have access to a mill and a lathe why not just make your own firing pin? Drill rod will more than adequate and if you're trying to make your gun a little shorter, the longer ar15 pin might not be the way to go. The ar15 firing pin tip is rather short which means you're pretty close to the bolt face when you drill out the firing pin channel from the back. A firing pin with a longer tip might make it easier to drill out the firing pin channel. You could make the pin to fit your bolt, and not the other way around.
 
#19 ·
What I did was grind off the front little pin part, and just made it use the slightly wider part. It removes the chrome plating but it doesn't matter that much as I used a non chromed one anyways.

The AR pin doesn't have a spring on it normally, the x25 primers are probably pretty hard, just like x39 primers. I have no trouble with an AR and commercial primers, putting a round in the chamber and dropping the bolt on it [worst case scenario] just leaves a tiny dimple not even the full diameter of the firing pin.

On my build I also used a spring, as .45 might have pretty soft primers. It is easy to drill a pocket in the back of the bolt for the large ring, to just the right depth for it to act as a stop, then drill a deeper hole in the same axis with a 1/4" bit for the spring.
Also you don't have to worry about the hammer coming to rest at the end of the firing pin's motion on an AR pin as that is how it works in an AR.
 
#25 ·
you don't have to worry about the hammer coming to rest at the end of the firing pin's motion on an AR pin as that is how it works in an AR.
I set up the firing pin in the suomi bolts I have done as an inetria firing pin for safety and legal reasons. If you have hammer follow and you don't have an inertia firing pin you are at a greater risk of having the round in the chamber going off. With an inertia setup the extra weight/pressure of the: firing pin; hammer; and hammer spring aren't all resting on the primer as the bolt closes, should you have hammer follow. This would also go a long ways to having a safer design that isn't "readily convertable" as even if you removed the hammer disconnector, using a inertia firing pin you aren't going to have enough energy in the hammer as it rides the bolt closed to set a round off.
 
#24 · (Edited)
I could just cut the front of a sunomi bolt off drill it for the firing pin and press it into a carreir made from square stock and pin it in place. I hate to rob a sunomi kit for the parts however.

I have started a bolt exactally like this for a suomi/thompson type build. So far I've drilled out the bolt (a gift from MTDEW)for a firing pin and cut the bolt down. I'm still debating if mild steel is going to wear well enough or should I use 4130 for the square bolt body. I suspect the mild steel will be fine since it will have a large bearing surface. I thought I may thread the bolt stub into the bolt body because I've set the back of the bolt stub as the hammer stop. I may be making more work for myself with trying to thread the bolt stub and very well may just end up using a couple 1/4" pins to keep it form being hammered loose. Here's a pic of it so far. For an extractor if you're going to make your own bolt, you might look through sarco and numrich to see if you can find a cheap pistol bar type extractor, pin and spring out of a gun like a S&W, beretta, or even a sten like you mentioned earlier. You might also want to look at the sgn-22 article where it shows how to make this style of extractor, although if you could get one for $10 I don't think I'd bother.
 

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#36 ·
Im on the fence as well about if a mild steel bolt will be okor the trunion for that matter.
...
Ill likley do a mild steel proof on design carrier first and see how it goes.
Perzackitly.

Use plain old chicken-wire grade 1018 or 1020 mild steel to prototype with. It's easy to machine and cheap. Use those to debug the design. Any deformation will tell you exactly where you need a harder metal, carburizing, or whatever.

I don't see that the trunnion would have to be anything other than mild steel; all it's doing is holding the barrel to the receiver. Unless you get radical skeletonizing it, it'll still be way stronger than the screws or rivets holding it to the receiver.

If the bolt slides back and forth like an AK bolt carrier, that's a lot of area to slide. That might not be an issue. You might need to heat treat the area where the hammer hits, or you might could just built it up a bit with some MIG weld and grind it back down; ordinary ER70 wire is a lot harder than mild steel.

(unsolicited advice) Build something that will fire reliably, then worry about how long it lasts before parts get peened, mushroomed, or egged. If you get too much invested in a particular design, it gets harder to backtrack and start over if you find a better way.
 
#27 ·
In the bolt stub above the hammer will be hitting the back of the stub so the only real wear on the mild steel parts will be from pushing the hammer down and smacking the bolt stop. If my bolt were a different design the front of the bolt could be the part that stops the bolts forward movement, but there's not much metal at the front of a suomi bolt compared to say a sten bolt. I might just go ahead and use some mild steel (a section of a 2" hitch) as a test piece and see how it goes. If it holds up, great! If not then I don't have anything invested except some time and an end mill or two as I got the hitch for free and I can remove the bolt stub from the mild steel body and reuse it.
As far as if a non-inertia firing pin would be legal or not I think the only people that could say for sure are the bafte boys. One of the ways they have ruled an ar15 with some m16 parts(or worn or broken ar15 parts) in it as a machine gun is if it has hammer follow (missing/broken disconnector or use of m16 trigger disconnector and selector for examples) and use 223 rounds with soft pistol primers the gun can be made to shoot auto. Even though doing so is very unsafe. I don't know what firing pin the 9mm version of the ar15 uses, but it has a different bolt and carrier so perhaps they have addressed the weight of the regular ar15 firing being able to set off 9mm rounds. In the sgn-9 articles the author Matthews stressed not to leave out a firing pin return spring as it would result in a possible run away full auto.
 
#28 ·
I have a pretty heavy firing pin spring, so I don't know if I'll have to go with the inertia type one, I'll just see what it does to a primed empty case if I take out the disconnector and drop the bolt on it. I can't imagine it'd fire the primer, but it might, so thanks for bringing that to my attention!
 
#33 ·
Well, I just remembered that I got a luger barrel for free because it has a ring in it, someone with a barrel wrench got a little excited... I'll make one of them 24Hr AKs, it'll be easy having a mill at my disposal. I figure if it ain't accurate it won't matter much, as the barrel was free and the materials wouldn't be all that much...

EDIT: The Orion's hammer guy is the one that made an AR lower out of a cutting board!
 
#37 ·
EDIT: The Orion's hammer guy is the one that made an AR lower out of a cutting board!
Someone over there made several out of wood. Not fancy wood either.

I have a tendency of over-think or over-design things. If you go down that route far enough, you will eventually complicate things enough that you just give up. Which is why I developed a new mantra: "Perfect is the enemy of good enough." The AK is a shining example of that philosophy.
 
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