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Thread: A question of chamber pressure?

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    Gunco Member jimmy_stikx's Avatar
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    Default A question of chamber pressure?

    What is the maximum chamber pressure a standard AKM trunnion and bolt can withstand?

    I have an AMD65 trunnion, bolt and carrier that I want to build up into a "wildcat" but am not sure what it can withstand.

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    Happy Camper hcpookie's Avatar
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    That, sir, is the $64,000 question.

    Find that out and you'll make many people happy!



    Look here (and elsewhere) for information about Yugo 8mm builds, .308 bolts vs. 7.62x39 bolts, etc. and some people (myself being one) are of the opinion that they will handle moderate .308 pressures.

    SAAMI recently altered their .308 pressure rating, so they began making .308 Saigas with 3 lugs vs. the standard 2-lug design. That's why I believe they can handle *moderate* pressures, at least by the new SAAMI standards. These standards are supposedly quite high, so they may very well handle *any* .308 pressures, but no one has been brave enough to try to destroy one yet.

    Others have made different chamberings up to .308 pressures with no ill effect. Yet.

    Most people are correctly choosing safety over anything else.
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    Gunco Good ole boy kernelkrink's Avatar
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    Chamber pressure has little bearing on lug strength. You also have "bolt thrust", which is the amount of force exerted rearward on the bolt by the cartridge. Chamber pressure in Lbs PSI X the square inches area of the chamber opening gives the amount of pressure exerted against the bolt and locking lugs. The .50 BMG chamber pressure of US milsurp ammo is around 54,000 psi. .223 is spec'ed at 55,000 max pressure. Similar chamber pressures, but I wouldn't want to use AR15 sized lugs on a .50! Even a lowly .22LR can have around 30,000 psi chamber pressure.

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    An interesting thing I learned last week while in Russia meeting with some of Russia's top firearms designers. One of them told me that the third lug was added to the Saiga-308 NOT for chamber pressure reasons but as an attempt to squeeze a little more accuracy out of the rifle.

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    No Hope For Me 1biggun's Avatar
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    An interesting thing I learned last week while in Russia meeting with some of Russia's top firearms designers. One of them told me that the third lug was added to the Saiga-308 NOT for chamber pressure reasons but as an attempt to squeeze a little more accuracy out of the rifle.

    HMMMMM so why dont they do it on all there rifles ands why are there reports from companys like those that make the Vepr that say it was because they fail the europran tests???


    as far as waht your amd trunion or bolt will handel I have loaded to were primers have pierced and the primers were flattened out. this is not a scientific estimet but lets just say the same primers in a 308 load that makes 60,000 PSI dont pierce or flatten out.

    If Personsaly try to keep things under a estimated 50,000 in 7.62x39 little is gained by going hotter. my 223 stuff is well over 50,000 PSI but aqs mentioned above base diamiter of a round affects bolt thrust. bolt thrust is what you need to be concerend about. a 7.62x39 load at 50,000 will hav e significantly less thrust than a 308 Win at 50,000 PSI .

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    Gunco Member jimmy_stikx's Avatar
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    I would be willing to do a stress test if I had another set of stuff to blow up, and a place to do it, but I think I'll stick to possibly doing a .30 rem, 6.8 spc or .35 rem. Thanks for the info.

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    Happy Camper hcpookie's Avatar
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    Kernel sorry I was so vague in my description, you're absolutely correct that bolt thrust is a key factor. As I recall bolt thrust is a direct result of chamber pressures (and surface area, etc) so I always start a "will it work" research on a caliber with the chamber pressure.

    That's interesting that the designers said that - I'm puzzled now as to where the "3rd lug for more strength" information came from. To be honest I don't really know where that info originated!


    I think any of those calibers will be a good choice. Personally I'd pick the 6.8
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    Indian Admin Winn R's Avatar
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    I took a pressure course or two in school but I'm in an area now I know nothing about.

    It would seem logical that the bolt/ chamber/ trunnion set up on an AK would be adequate for anything a cartridge could stand... the limit would be the over pressure indicators in the casing rather than design strengths in the weapon.

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    Gunco Member jimmy_stikx's Avatar
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    My next concern would be usable mags, but I should find a barrel first.

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    No Hope For Me 1biggun's Avatar
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    well the first thing is to decide what you want. its kind of hard to help if you dont know what calibure or OAL of round you want and what you are trying to do with it.

    if it it fits in a Ak length mag well then chances are a 7.62, 223 or 5.45 mag can be made to work if it dont then you got to go with a .308 mag and mod it likely. the 35 remington can not. a 308 will out do the 30 RAR so why not just build that and be able to get ammo. remington wil likley abondon that in a year or so just like they did with the 6.8 SPC.. if you wantg a better round than the 6.8 then just build a 7mm-08 loaded light. the 35 remington is a good idea and one I have looked at. it can be done but why?? will you use it for some thing a 308 cant do?? what are you goals? there is several rounds simular like the 358 Win. I have considerd a 35 rem or 358 win myself both will take a longer mag like those used for a 308 win.

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