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Thread: 308 ak

  1. #121
    Gunco Regular Gunter's Avatar
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    Today I did some measuring between a 7.62 AMD, 7.62 Romy, and a 5.45 Bulg. bolt lugs. The AMD and Romy were within .001 of each other so we will just call them the same. The 5.45 has the smaller stem then the 7.62. What I'll call the small lug is the one away from the extractor. The width and height are the same between them on either caliber. The difference is in the length. The AMD/Romy is .402 long and the 5.45 is .551 long. The large lug where the extractor is located is .611 long on the AMD/Romy and .720 long on the 5.45. The bolt face hole on the AMD/Romy is .458 and the 5.45 is .400. Both would need to be opened to around .475 for the 308.

    Rbthntr64, does that sound like the measurements on the Vepr? Also didn't the Saiga 308 use a small stem bolt?

  2. #122
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    Math isn't my greatest subject either so, someone check these figures.

    In the other thread 1biggun asked about bolt thrust at 42,000 cup on a .308 and 50,000 cup on a 7.62x39. I found a formula to convert cup to psi. Now this will only be a ballpark figure as there are +/- in both cup and psi. So hitting either end of the +/- could give different results. The formula is Cup x 1.516 -17902 = PSI. So, taking your .308 at 42,000 cup should be around 45,770 psi. The 7.62 at 50,000 cup should be around 57,898 psi. Now we need to figure the square inch we have touching the bolt head. The .308 is .473 inch across so, the radius is .2365. We take .2365x.2365x3.14=.175 square inch of area (I think). The 7.62 is .444 inch across so the radius is .222. So .222x.222x3.14= .154 square inch of area. Now we can take the psi x the area to find the amount of pressure on the bolt. For the .308 at 42,000cup/45,7700psi the force on the bolt is 8009 pounds. The 7.62 at 50,000/57,898psi the force is 8916 pounds. If we bumped the .308 up to 60,000 psi the force is 10,500 pounds. Now none of these figures take in to account the friction between the brass case and steel camber. These are just pressure figures at a certain pressure on a certain area.

  3. #123
    No Hope For Me 1biggun's Avatar
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    xxx
    Last edited by 1biggun; 03-06-2016 at 10:35 PM.

  4. #124
    Gunco Regular pupwag's Avatar
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    Saiga 308 uses the small stem.Extractor side lug is the same as Bulgy 74 ~.720.The ejector side lug is .100 longer on the 308-.645.Most of that is a ramp to help rotate the bolt.Bolt face hole looks like .478.Bottom part that strips the rounds is the same as a 47 width/depth wise, of course the Saiga has the little (third)sorta lug projecting down off the rear left side .The Saiga bolt was ~.050 wider across the two main lugs with little reliefs cut into the lugs to clear the upper rails as it would have been to wide to fit the ~.980 width opening for the bolt carrier.It would not enter a regular AK trunnion until I milled off the .025 per side in a rotary table.
    It's only metal, it's not magic.

  5. #125
    No Hope For Me 1biggun's Avatar
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    xxx
    Last edited by 1biggun; 03-06-2016 at 10:35 PM.

  6. #126
    Gunco Member bert01's Avatar
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    im going to talk with a couple of the engineers tomorrow at work and get them to do some calculations with the trunnions and bolts and see if they can come up with some shear numbers for the parts. ill post what they come up with asap, they do this stuff every day for industrial equipment, and i would put a lot of faith in whatever they come up with

    then we can compare those numbers to the bolt thrust numbers we've come up with

    has anyone tried to find out what kind of numbers the "strict european pressure tests" used in deciding the romy 308's couldnt be sold to the public

  7. #127
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    Here's a link to the pdf article on the cup/psi conversion if you want to take a look at it.

    www.shootingsoftware.com/ftp/psicuparticle2.pdf

    I'm not an engineer, don't play one on tv, and didn't stay at a Holiday Inn Express last night, so take the above info with a grain of salt. Bert01's engineers may say that everything is BS. I know that there is software out there that the engineers can use to test stress and how a metal will hold up over a certain number of duty cycles. Maybe we can get some help in sorting all this out.

    Looking at the different calibers:

    The 5.45 pushes a 60 grain bullet at around 2900fps. Surface area is around .120 square inch.

    The 7.62 pushes a 123 grain at around 2350fps.

    The .308 pushes a 147 grain at around 2800fps.

    These are the figures for the 7.62 and .308 are from PCM, UMC, Winchester white box, and American Eagle as these are probably the ammo that someone would just walk in and buy at the store. If we could find the pressures that these rounds are running then that might give us a chance to compare apples to apples. Does anyone know the data on the Yugo .308 ammo?

  8. #128
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    Here's a link about the CIP and SAAMI standards for 9mm. It goes into some detail about the two. The CIP lists their loads as MPa (which 1 MPa = 145.0377psi), but the post states that you should not convert the two.

  9. #129
    No Hope For Me 1biggun's Avatar
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    xxx
    Last edited by 1biggun; 03-06-2016 at 10:36 PM.

  10. #130
    Gunco Member bert01's Avatar
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    sorry for the long post just trying to get it easy to read, got some of the info from www.thegunzone.com/30cal.html trying to do everything on the safe side hence the max proof pressures for the 308 stuff and the bolt head diameter instead of the true case head diameter

    i got some good solid works 3D models of a romy trunnion today trying to run the force application on it as we speak (test how the lugs will hold up under different pressures applied from the bolt thrust)

    not having much luck the software im using doesnt allow for heat treated steel so even the opperating pressures of the 7.62 x 39 arent giving safe results in the solid model stuff

    ill keep trying and let you know what happens


    Bolt thrust= area x psi

    Area = 3.146 x ( (case head diameter / 2)^2)

    Above is from http://www.riflebarrels.com/articles...g_strength.htm


    7.62 x 51 NATO

    "Proof" pressure = 67,500 psi
    Bolt head diameter = .475

    3.146 x ((.475 / 2)^2) = .1772

    67,500 x .1772 = +/- 12,000

    7.62 x 51 NATO = +/- 12,000 lbs bolt thrust max

    308 Winchester

    "Proof" pressure = 83,000 psi
    Bolt head diameter = .475

    3.146 x ((.475 / 2)^2) = .1772

    83,000 x .1772 = +/- 14,800

    308 Winchester = +/- 14,800 lbs bolt thrust max

    7.62 x 39

    Max "reload" pressure = 45,000 psi
    bolt head diameter = .458

    3.146 x ((.458 / 2)^2) = .1647

    45,000 x .1647 = +/- 7,420

    7.62 x 39 = +/- 7,420 lbs bolt thrust

    6.5 Grendel

    Case head diameter = .445

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