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Thread: Gas op 7.62x25mm

  1. #1
    Gunco Member Bullpup's Avatar
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    Default Gas op 7.62x25mm

    Bought myself a 7.62x25mm barrel to fit a 22mm trunion. I plan to have it turned down a bit to accept a rear sight block as well. I'm leaning in one of two ways as what to do next. Either:
    A. put a gas block in the usual place and build a pump action Ak in 7.62x25mm. This has it's advantages in that it would be pretty easy for me to do, wouldn't require any permanent alteration to the barrel or welding of the bolt, front trunion etc... And that it will cycle any loads, including those neat subsonics loaded with 150gr bullets in the x25mm case. If I want to make it semi auto later on, it should still be possible.

    B. Make it gas operated with a short gas system. I don't want to do blowback because of the amount of welding needed, and it's irreversible. I would want the gas block at about the same place as a krinkov. Ideally I would like to use regular length handguards, so maybe just slightly longer than a krink, though I would run into problems with the HG retainer. I think with a short gas system, shortened recoil spring, and maybe a bit of weight shaved off the carrier, I could get it to work. The only irreversible part is the carrier.

    So which sounds like a better idea? I'd rather have a semi auto, but I'm concerned it won't work. I've studdied the gas op-7.62x25mm Ak PBB built, and I'm hoping by taping the gas closer to the chamber with the same dia gas port, and a shorter lighter piston, that I can get away with removing less weight from the carrier. My only hesitation is removing that hump from the very back of the carrier, since it keeps the hammer from striking the carrier before its fully in battery... I want to keep that intact.

  2. #2
    Gunco Member Bullpup's Avatar
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    looks like all those reply posts got eaten? anyhow I've decided not to do a tiny RPK with this build. I can't scare up the GB, FSB, bipod and RSB at a reasonable price, and I'm leaning in a different direction now anyway. I'm trying to wrangle up a Yugo gasblock with the gas cutoff, so I can tune the rifle to fire regular 85 grain 7.62x25mm ammo in semi auto mode, or switch the gas off and fire heavy 150 gr. subsonic loads with a manual action. I'm going for about a 3" gas piston and a very short gas system with a regular akm size gasport. what I can't decide now is wether to weld the front sight post to the gasblock for a short sight raidus or to put the FSB all the way at the end of the 18" barrel, which will look odd with such a short gas system.

  3. #3
    redchevyman's Avatar
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    the sight at the end of the barrel will give you a better sight radius for accuracy. It will also be easy compared to welding it to the gas block.
    Buy your US made AK-47 compliance parts here.
    Best price on US made AK parts! also $5 flat rate shipping .
    http://www.rcmgunparts.com/

  4. #4
    Gunco Member waynewool's Avatar
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    Please help me out. I have never worked on a conversion such as this, so bear with me. By blowback operation; do you mean that the gas piston is removed and the gas directly blows back the action/bolt? or what does it mean? Doesn't it makemore blowback in the operators face?

    What are the advantages/disadvantages of blowback operation?

    Has anyone figured out the right combination of parts, barrel length, bolt lightening, spring tension or spring removal to get a 7.62x25 conversion to work without blowback operation?
    Thanks

  5. #5
    Gunco Member Bullpup's Avatar
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    first off I'd recomend you do a lot more reading before tackling a project like this, get at least one regular Ak build under your belt first.

    Blowback (arms) - Wikipedia, the free encyclopedia

    An ak is gas piston operated. the bolt locks into the trunion, after firing a round, gas from the barrel has pushed the piston (and bolt carrier) backwards, unlocking the bolt. the bolt and carrier travel backwards, ejecting the spent shell and stirpping a new one.

    most pistols, submachine guns, semi auto .22's and pistol caliber carbines are blowback operated. This means the bolt never locks. The bolt is heavy and kept forward by the recoil spring. When the round fires, the empty casing pushes backwards with the same pressure the bullet experiences as it is pushed forward. the inertia of the heavy bolt sends the bolt backwards at a reasonable speed, ejecting the spent round and stripping a new one. if you use too big of a cartidge, blowback wont work, the bolt will just be moving too fast, or will need to be way to heavy to be reasonable.

    7.62x25mm is like a big pistol round or a very small rifle round. it is just at the border where you could use gas operation, most people opt for the use of blowback.

    http://www.gunco.net/forums/f244/7-6...bl-pics-27165/

    http://www.gunco.net/forums/f3/amd-b.../?=#post352753

    Panaceabeachbum built a sucessfull gas operated 7.62x25mm ak, you can see what was nessicary to get it to cycle from his posts. In a PM he added this advice: "... I cut a larger chamfer on the bolts locking lugs so it wouldn't have to rotate as far to begin unlocking."

    the other key points are:
    *smooth up rails and all friction surfaces
    *reduce carrier weight
    *shorten recoil spring
    *weaken hammer spring
    *plug gas vent holes in gas block

    Other options I think would work:
    * tap gas closer to the chamber
    * larger gas port

    Somewhere within these options is a healthy balance for operation. PBB got his to work.

  6. #6
    aka: SDK1968 dutigaf's Avatar
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    AZHONKEY is the man on this build.

    his conversions are real works of art. not to mention they run perfect.
    say what you mean & mean what you say


  7. #7
    Gunco Member waynewool's Avatar
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    Thanks for the advice so far. The bolt and recoil spring must be from AK74 because the base and shell dimensions are closer to 5.45x39 than 7.62x39 and the recoil spril is lighter to begin with, correct? Also, if for a true blowback operation, would it be better to weld or seal the hole in the barrel that enters the gas tube/block? What do you do with the operating/gas rod? Do you leave it in place even though they are not used for that purpose or could you remove the op rod which removes additional weight that must be pushed rearward for the cycling of spent to new shell?

    Thanks Again

  8. #8
    Gunco Member waynewool's Avatar
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    Oh I forgot to ask. Does someone have a link showing extensive photos and documentation of the steps listed in some of the above posts? I would like to see as many photos as possible. I would like to see close ups of the pictures of the "cut a larger chamfer on the bolts locking lugs so it wouldn't have to rotate as far to begin unlocking."

    Thanks

  9. #9
    tired of idiots vz58's Avatar
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    Wayne, you can use a 223 bolt as the face is close. There shouldnt be a hole in the barrel as you will need a barrel made or buy a 762x25 barrel from another gun (no hole there too) you can do away with the gas piston. Then you need to fix the bolt to the carrier and remove the locking shoulders on the trunnion or make a new one with out locking shoulders. Look around for the thread on the 45 acp blowback to see good details on a similar build.

  10. #10
    Gunco Member Bullpup's Avatar
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    Wayne, you a mixing up what is being said. You won't need to alter your locking lugs on the bolt for a blowback operated rifle, you won't need locking lugs at all. here's some more reading on the subject of blowback rifles:

    The Guns Network LLC ~ Discussion Forums

    http://www.gunco.net/forums/f244/wha...version-31962/

    The Guns Network LLC ~ Discussion Forums

    The Guns Network LLC ~ Discussion Forums

    The Guns Network LLC ~ Discussion Forums

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