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Thread: build your own FN P90

  1. #21
    Happy Camper hcpookie's Avatar
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    OK, the recoil spring that pushes the bolt forward is a heavier spring than that which keeps the barrel in place. I haven't looked at it closely enough but the basic idea is that the barrel "floats" and it moves that small amount (.030" which is less than 1mm) before the spring is overcome by the recoil forces acting against the case. The whole thing is remiscent of the Russian's Abakan design where the barrel floats on a carriage.

    If you look at those super-slow motion gunshot pictures you'll see the bullet is already downrange before any of the recoil forces can act on the gun and shooter. Inertia, baby!

    Also, FN coats the P90 cases with a clearcoat that has slippery qualities to aid in extraction. Quite possible this is not needed on a semi-only gun but it is a voodoo subject right now since no one can figure out what it is to replicate it. Personally I plan to dry lube all of my reloads but it is worth mentioning as this may assist in the extraction on this blowback system.

    If I were to make one I would definitely try to imitate the delay system somehow, or use a gas-operated system to avoid the blowback issues altogether. Perhaps using .22 Hornet or some other similar type of round.

    Or just build one of these





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    http://pookieweb.net


    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
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  2. #22
    TRX
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    [description] Yes, but it's hard to make all that out from the crummy low-resolution pictures at the URL.

    It wouldn't be difficult to float the barrel so it could move in recoil. I need to figure the case head thrust for the 9mm and 10mm, which were both used in straight-blowback arms, and compare it to the 5.7.

    I really don't need yet another project, but I'm awfully tempted to buy that airsoft shell... with my luck it'd be "off" enough not to accept a real P90 magazine.

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    Quote Originally Posted by hcpookie View Post
    Also, FN coats the P90 cases with a clearcoat that has slippery qualities to aid in extraction. Quite possible this is not needed on a semi-only gun but it is a voodoo subject right now since no one can figure out what it is to replicate it. Personally I plan to dry lube all of my reloads but it is worth mentioning as this may assist in the extraction on this blowback system.
    The coating was for the pistol IIRC, guys were saying the cases would work in the PS90 after being loaded enough times to wear the coating off.
    I really don't need yet another project, but I'm awfully tempted to buy that airsoft shell... with my luck it'd be "off" enough not to accept a real P90 magazine.
    I bought one, it will not accept a real P90 mag, well, it might with modification, but the mag latch is cheap and crappy, mine broke within 10 mag changes... Also, the whole thing is really crappy plastic moldings. Don't expect any kind of zero retention with the "well" brand airsoft body.

  4. #24
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    There's a thread on Weapons Guild about doing a homebuilt inside an airsoft shell.

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  5. #25
    Happy Camper hcpookie's Avatar
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    Just buy a real stock - this guy is selling just the stock!

    FN P90 PS-90 Stock NEW BLACK : Other at GunBroker.com
    Gunco Member #10

    http://pookieweb.net


    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
    http://pookieweb.net/pink/pink.htm

  6. #26
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    Cool... but with a starting price of $420, it'd be more reasonable just to save my shekels and buy a real P90.

  7. #27
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    I bought a magazine from CDNN last year, on sale for $19.95, just to see how the helical ramp thingie worked.

    The Amazon page with the "Well" P90 airsoft has been up in a spare browser tab for months. Yesterday the price dropped from $30.28 to $28.95. What the hell, $5.99 shipping, I went for it. If it's as flimsy as reported I guess I can layer some carbon fiber inside it.

    Green Mountain has 1:7 twist .223 blanks for $33. I guess that's the next step.

  8. #28
    Gunco Addicted for life j427x's Avatar
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    i wonder if 7.62x25 will feed from the mag? LOL!

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    Quote Originally Posted by j427x View Post
    i wonder if 7.62x25 will feed from the mag? LOL!
    No, too large of a base diameter and way too much taper. There was a guy over on weapguild that was thinking on that, but I haven't been back in a long time, my bets are that it didn't go anywhere...

  10. #30
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    No, that thread died out.

    For some demented reason brand new, brass cased, Boxer-primed 5.7 ammo is incredibly cheap now... less than what I've been paying for empty brass in some calibers. For reloading, jacketed .223 bullets are as cheap as it gets.

    I like caliber conversions, but honestly, as cheap and available as 5.7 is, and the fact that it's the only thing that fits the unique P90 magazine, you'd be crazy to switch away.

    There are some P90-ish variants that have a regular magazine hanging below the buttstock. I think I'd look into building a copy of one of those before I'd try serious hackery on the P90 magazine.

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