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Thread: Blowback Head Space x25 Conversions

  1. #11
    aka: SDK1968 dutigaf's Avatar
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    ha ha......... nothing slides by you two does it?

    its one of the reasons i like this forum.... good natured people who like to actually BUILD and talk about building guns.

    the reamer for 7.62x25 TOK is not cheap. ive "borrowed" one before.... and ive heard talk that some of the "real" fancy machinists use that another reamer but it is a shade different and then its a "feel" thing.... which would kinda defeat the point of making the change if you were still guessing at it.

    and yep thats why the subby's are so heavy. takes a heavy bolt for that hot little round, which is why im wanting to use a PPS43 or 41 bolt on the modified carrier... to gain that weight.

    gonna be a winter time project when things are slower...

    sdk
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  2. #12
    No Hope For Me Coils's Avatar
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    Two comments, don't know if they will help though.

    1-you have to remember the PPSH41 barrel is chrome lined, that might cause problems using a reamer?

    2- I dug out my unmodded PPSH41 bolt and inserted a spent case, the bolt surrounds the base of the case up to the front of the extraction groove, in the pic this is about where the red line is. Click on the pic for a larger image
    I can't compair it to the barrel because it's not here right now, but I'll do what I can when it is.
    Now I'm guessing but this gap might close a little more when the heavy bolt slams against the round pushing it further into the chamber some.
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  3. #13
    Gunco Regular Gunter's Avatar
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    Winn, that is the reason that I chose not to use a subgun barrel that I had. I can say for a fact that a .308 blank that is chambered with a 30 Mauser reamer will shoot 7.62x25. I just cut the chamber until there was .005-.006 clearence between the AK bolt face (no extractor) and the barrel face using a dummy round. Then set everything so that there was about .002 headspace.
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  4. #14
    Indian Admin Winn R's Avatar
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    Quote Originally Posted by dutigaf View Post
    ha ha......... nothing slides by you two does it?

    its one of the reasons i like this forum.... good natured people who like to actually BUILD and talk about building guns.

    the reamer for 7.62x25 TOK is not cheap. ive "borrowed" one before.... and ive heard talk that some of the "real" fancy machinists use that another reamer

    sdk
    "real" fancy machinists -- Well Sean, I guess that leaves me out!


    Quote Originally Posted by Coils View Post
    Two comments, don't know if they will help though.

    1-you have to remember the PPSH41 barrel is chrome lined, that might cause problems using a reamer?
    No -- I didn't know that. Like an idiot, I looked at the ones I've got and thought how lucky I was they were like new. That does however save me the reamer cost!

    Quote Originally Posted by Coils View Post
    Now I'm guessing but this gap might close a little more when the heavy bolt slams against the round pushing it further into the chamber some.
    I think it does close a little more but from the comments above still has a tendency to blow cases. I want a gun my middle school children can shoot.



    Quote Originally Posted by Gunter View Post
    Winn, that is the reason that I chose not to use a subgun barrel that I had. I can say for a fact that a .308 blank that is chambered with a 30 Mauser reamer will shoot 7.62x25. I just cut the chamber until there was .005-.006 clearence between the AK bolt face (no extractor) and the barrel face using a dummy round. Then set everything so that there was about .002 headspace.
    Thanks Gunter, that is the solution I had in mind. A casing supported is a casing that won't split.

    I wonder now, given the chromed chamber, if I should look again at cutting into the '74 bolt face. Dutigaf's comment above is well taken, the slop around the extractor could cause problems. Maybe.. I'll assume.. (boy this is getting me in deep) that the blowback operation would minimize extractor related problems.

    Or, and I really don't want to go here, I could tig material to the breech face, or weld on a washer, then turn it down to get Gunter's numbers.

    What do you guys think?
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  5. #15
    No Hope For Me 1biggun's Avatar
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    I have about $150 into my reamer with the extra pilots that I got to do from .307-.310 bores. I cant cut a chrome chamber .

    the 30 mauser is slightly differant but it will work it may not however be as accurate or treat the brass as good if reloading comercal is a concern.

    from what Ive read and already seen most of the surplus splits necks I have several of the rommy split from were its crimped in my 45-70 addapter. I have no neck bulging but in the addpter its flush with not protrusion.

    I dont think cutting the bolt face will offfer any real advantage as the case is still unsuported by the chamber. the bolt face is larger than the round and the round tapers any way. it may help redirect a failure but it is not going to reduce or prevent one. alsoif the bolt face is cut it will place the ejector to far forward un less its modifed.

    I can cut or lengthen a chamber on a Non chromed lined barrel and Im looking for work. I have no idea how many chambers a reamer will do before it needs to be sharpend or replaced. If some one wants some thing done PM me. I was going to sell some chamberd blanks but Im looking for a cheap source of blanks or take off barrels. I have a few remington n winchester take offf barrels but they were not super cheap so it is hard to offer a cheap chamberd blank.

    My build will have a deeply seated chamber and a extractor cut. I want to be able to relaod brass in the future if the surpluss dissapears or gets out lawed. also accuracy is going to be better with a fully seated round that isint bulging or bursting. as long as it ejects Im ok.

  6. #16
    No Hope For Me 1biggun's Avatar
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    I just cut the chamber until there was .005-.006 clearence between the AK bolt face (no extractor) and the barrel face using a dummy round. Then set everything so that there was about .002 headspace.
    sounds right to me. I am doing a gas operated AMD 65 like that now. well at least the barrel I have to many projects and no cash.

  7. #17
    gunco irregular moleman's Avatar
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    Here's a 9mm winchester ranger (black talon) that ballooned at the feed ramp bevel. The back side where there is no bevel is fine. It happened when a temporary recoil spring took a set and did not close the bolt completely. I was suprised that the case balloned out that much but did not rupture. I wonder if a steel case would do the same or if thats why people are reporting so many split cases with the 762x25? I would try to get as little of the case exposed as possible.
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  8. #18
    No Hope For Me 1biggun's Avatar
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    Im wondering if to light of a bolt is allowing some of the builds to have issues as well? possably being blown part way out of the chamber before the pressure drops off??

    Id like to come up with a way to prevent a out of battery fire. some sort of a acuater that only allows the the pin to be exposed whn the bolt is fully forward or or a trigger block that does the same. It cant be that hard. to be honest a the thought of a slam fire or a accidental douple or bump fire that lets the hammer ride the bolt home or relase on it way home or to fire on a partualy chamberd round scares the hell out of me. I wonder if there is a way to profile the bolt or hammer so it can only hit the pin at the vary last part of the bolt travel?? sort of l;ike the tail on a ak carrier but one that the hammer would hit untill the carrer is at least 90% forward. there has to be a easy way.

  9. #19
    No Hope For Me 1biggun's Avatar
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    I see a way it cold be done with a rod piviots that runs under the rail that as the bolt moves back would make it impossable to pull the trigger that that once the bolt returns the rod wold pivot back with spring pressure to allow it to release again .. I have no real idea hoow the full auto parts work or if this might some how duplicate them in some way and be considerd illeagle but I can see it being made to work with a AK trigger system. it wouuld not affect the disconector it would simply act like a saftey unless the bolt was closed. it would have a zone were the bolt is setting the trigger were the trigger could be pulled but as the bolt returns forward and the hammer is not being hled down by the bolt it would again bar the trigger. I think it would workit would require three pieces a bar a pivot and a spring.

  10. #20
    gunco irregular moleman's Avatar
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    Quote Originally Posted by 1biggun View Post
    Im wondering if to light of a bolt is allowing some of the builds to have issues as well? possably being blown part way out of the chamber before the pressure drops off??

    Id like to come up with a way to prevent a out of battery fire. some sort of a acuater that only allows the the pin to be exposed whn the bolt is fully forward or or a trigger block that does the same. It cant be that hard. to be honest a the thought of a slam fire or a accidental douple or bump fire that lets the hammer ride the bolt home or relase on it way home or to fire on a partualy chamberd round scares the hell out of me. I wonder if there is a way to profile the bolt or hammer so it can only hit the pin at the vary last part of the bolt travel?? sort of l;ike the tail on a ak carrier but one that the hammer would hit untill the carrer is at least 90% forward. there has to be a easy way.
    most of the subgun bolts that get converted to semi end up lighter than what they started out at. They also don't have the extra kenetic energy of the bolt moving forward and the fixed firing pin setting off the round before the bolt closes.
    As far as profiling the bolt so it can't set off a round, I'd almost think it should be as round as possible to ease the bolt down. Otherwise it would close faster on a 90 degree edge I'd think. The ar15 firing pin I use in my suomi conversions is set up as an inertia firing pin. With the hammer all the way down there is still at least a 1/16" gap before the firing pin starts to touch the primer plus the heavy firing pin return spring. When I was testing the design I took the disconnector out of the trigger group and tried to get a test round (no powder hole in bullet nose) to set off a primer or leave a dent in the test round primer. I settled on a combination that gave reliabale ignition, but would only slightly mark a soft remington primer (about the same amount as an ar15 does chambering a round) in case of hammer follow.
    Using a different design or modifying the disconector on an ar15 or ak47 so that it won't release the hammer from the disconnector to the trigger unless the bolt is fully closed would get you this safety. Figuring out the linkage would be the pisser there, as well as making it legal like 1Biggun said. The remington 870 style hammer and sear I'm using could very easily be adapted to for this and actually has theat feature in the comercial remington guns.

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