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Thread: scratch build 7.62x25 on ak reciver blow back

  1. #21
    TRX
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    Gunco Irregular TRX's Avatar
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    Quote Originally Posted by [486] View Post
    It would be easy to use an AK extractor if you have a mill.
    Without a mill, you could hacksaw a slot in the side of the bolt and use a thin extractor. The AK has a big military-style extractor designed to positively yank dirty or damaged cases out of the chamber. Many modern hunting rifles use much thinner extractors, basically pieces of sheet metal. They do this to provide more support for the case head for high pressure cartridges. Might not be a bad idea for a blowback, particularly since the extractor is only to remove an unfired cartridge from the chamber; the blowback spits the fired case out.

  2. #22
    No Hope For Me 1biggun's Avatar
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    Ive been looking at evey gun I have including some 22lr a strip of spring steel bent at a 90 held in a groove with a pin or circular ring or collar is all it would take the sunomie piece comes to mind. im studying the sten extractor as well pretty simple set up are Sten extractors avaliable cheap any were???? 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.

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    Gunco Veteran muttman's Avatar
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    big gun,
    try and looking up a cz52 extractor on gunbroker they are not high $$ and common right now. muttman

  4. #24
    gunco irregular moleman's Avatar
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    Quote Originally Posted by 1biggun View Post
    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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    Last edited by moleman; 08-05-2009 at 10:38 AM.

  5. #25
    gunco irregular moleman's Avatar
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    Quote Originally Posted by [486] View Post
    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.

  6. #26
    No Hope For Me 1biggun's Avatar
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    I set up the firing pin in the suomi bolts I have done as an inetria firing pin for safety and legal reasons
    HMMMM is a non inertia firing pin legal in this set up? I had not though about it. A inertia pin does seem safer.

    Im on the fence as well about if a mild steel bolt will be okor the trunion for that matter. Im concerned about were it hits the hammer and Im worried about were it will hit the trunion when it comes to rest on a empty chamber. Im not sure screwing the bolt in it the way to go unless. that part takes a hell of a beating im afraid the the threads will loosen or stretch with all the pounding and heat. I was envisioning pressing it into the carrier with a press fit and then cross pining it.

    Ill likley do a mild steel proof on design carrier first and see how it goes. I have no way to temper a carrier even if I did build one in 4130. some thing that big would likely take a forge and other stuff. Now if a meamber here or some one localy could inexpensivly do the tempering then that might be a option. since its basicaly is a solid block with a few groves and holes I dont thing it would warp much. If it can be machined first then temperd it would be a plus.

  7. #27
    gunco irregular moleman's Avatar
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    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.

  8. #28
    Gunco Veteran [486]'s Avatar
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    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!

  9. #29
    No Hope For Me 1biggun's Avatar
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    hmmmmm ive been looking at these for a day they cost under $3. Im not planing on using a normal carrier but was thinking what if? I see Kvar is out of 223 and 5.45 bolts Is there a nother source for them????????
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  10. #30
    gunco irregular moleman's Avatar
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    Take a look at a pps43 bolt. I think you could cut that bolt face shape out of square stock pretty easy. For an extractor sarco has a beretta 92 extractor, spring, and pin for $9.50. Beretta M9 / M92 9MM

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