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Thread: Maadi-Griffin build

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    Default Maadi-Griffin build

    This started in Ed Hubel's 12gaFH thread, but I'm starting a separate thread here since it's a specific rifle build instead of discussion about his 12gaFH cartridge.

    Ed's thread: http://www.gunco.net/forums/f113/12g...l?=#post591946

    I've liked the Maadi-Griffin ever since I first saw a picture. It's a bullpup .50 BMG. The company sold them as complete rifles, kits, or plans. None of the above are still available, but acquired the plans from a web torrent. The scan was poor but readable.

    Basically, you need 7" of 2" diameter 4140, 5" of 1-1/2" diameter 4350, a few feet of square and round tubing, some music wire, a bit of flat stock, and a few odds and ends from the scrap box. I figure the metal would run under $100 even if you had to buy it from Aircraft Spruce or Online Metals.

    Unfortunately, the ex-military .50 barrels have gone from $50-ish to $300-ish, and though I looked at the plans from time to time, I have other projects that need my discretionary entertainment funds more.

    The Voices told me if a Maadi is .50 was cool, a Maadi in 12gaFH would be even cooler. I laughed at them in derision.

    I just won a rifled 12 guage barrel blank, 27.5" long, from Gunbroker, for $129.

    Looks like the Voices got the last laugh.

    I don't remember where I got the pictures, but these are completed Maadi-Griffins. One builder chose not to use the AUG-ish handguard, but the guard is correct for the Maadi design. The bottom picture is from the cover of the plan book.

    Yes, that's the bolt handle by the buttpad. The buttpad is attached to the end of the bolt, and they both come out of the receiver together, with the fired cartridge held by the extractor. You clip another cartridge on, then twist the buttpad back into place.

    The basic design is adaptable to a more conventional layout by moving the bolt forward and providing some space for it to move, but then you increase the length of the rifle.
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    These are the four major parts, 90% of the machine work, and all of the complicated bits.

    1) This is a "fat bolt" design, meaning the bolt body is larger than the locking lugs. The bolt is drilled for the firing pin, necked down for the lugs, and the lugs are shaped by making two parallel cuts and rounding the corners. Mostly lathe work, with the flats for the lugs milled. The round ends of the lugs could be done on the mill with a rotary table, or for that matter with a belt sander and a steady hand.

    2) The receiver is bored from each end, with a web at the barrel end. The web is drilled, then cut away for the locking lugs. The Maadi uses round lugs instead of square, so you just jog left and right for the cuts, no big deal. My Gorton mill should have just enough Z clearance to make the cuts, but if it doesn't, I can make a fixture to hold the receiver on the lathe cross-slide and put an end mill in a collet.

    The barrel end has to be threaded for the barrel. I hate single-point threading, but it will build character, I guess.

    3) The locking ring is thickwall stock, threaded. It's the jam nut for the barrel, like a Savage bolt-action rifle.

    4) The barrel has to be threaded.
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    Maadi receiver drawings. The cut in the web isn't a true radius, but it can be cut with an end mill and then shaped by hand if necessary.
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    Maadi bolt. Fairly straightward.
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    Completed rifle and subassemblies. This one is a later production model with the cast aluminum lower, which forms the pistol grip, guard, and box for the trigger bar. The trigger bar is just above it, then the barrel and shroud assembly.

    Two pip pins hold it together.
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    Trigger bits. All of the springs are wound from music wire.

    It took me a bit to figure out what the "trigger bar" setup was. Basically, all the trigger bits go into the trigger bar, which then floats inside the lower. It packages all the bits neatly, and there's no change in their relationship if the rifle is dismantled and then put back together.
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    Barrel and shroud pieces. This is the only major piece of hand-waving I've found so far. The shroud apparently floats loosely between the barrel nut and shround ring. The ring apparently presses on. I'll probably do something a bit different here.
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    One of Ed's pictures:

    .50 BMG brass to the left, partially fireformed, then a finished FH case. One of his buddies CNCs threads onto the extractor groove area, then they have CNC'd rings that screw on with Loctite. I have a couple of these I bought from Ed a year or so ago. Physically, it's the same diameter as a 12 gauge shotgun shell but slightly longer. The far right is a raw 3.5" case that was never crimped, I think.

    RMC made a run of "billet" FH brass recently, but cases turned from bar stock aren't as strong as the forged BMG brass. Though honestly, I don't plan on loading high enough for it to matter.
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    (sorry, the message editor seems to eat spaces, so it's all run together instead in columns like I wrote it...)

    Bill of Materials:

    Trigger Bar Assembly
    Part #
    1 trigger bar 3/4x16ga sq. tbg 16-1/4"
    2 sear 4140 1/4x1" flat
    3 sear spring .040" x 10" music wire
    4 sear pin .156" drill rod .80"
    5 sear link 4140 1/4x1" flat
    6 sear link spacer spring .040" x 10" music wire
    (also called sear link spring)
    7 sear link pin .156" drill rod .80"
    8 trigger 4140 1/4x1" flat
    9 trigger spring .040" x 10" music wire
    10 trigger pin .156" drill rod .80"
    11 actuator rod .156" drill rod 14-1/8"


    Bolt Assembly
    Part #
    12 bolt 1-1/2" dia. x 4-1/2" 4340
    13 bolt handle 3/4" dia. x 2.4" lg. CRS
    14 bolt handle set screw 5/16 x 5/8 UNF
    15 firing pin 9/16" dia. x 5" 4140
    16 firing pin tail stock 9/16" x 1.281 x 3/4 4140
    17 firing pin spring .100" music wire, x? lg.
    18 bolt cap 1.875" dia. x 1.375" 4140
    19 butt plate 1/8 x 1.7 x 5-7/8 HRS
    20 butt pad high density foam rubber
    5-3/4 x 1-3/4 x 1-1/2"
    * 21 butt pad cover 62 durometer urethane
    6-1/8 x 2 x 1-3/4"

    Barrel Assembly
    Part #
    22 barrel (purchase)
    * 23 (a) muzzle brake 1.5x4 10ga CRS tbg.
    (b) ? round bar, mounting ring
    24 forward shroud ring 1.87 OD 1.37 ID 1.5 lg. CRS
    25 barrel lock ring 1.87 OD 1.415 ID .850 lg. CRS
    26 barrel shroud 2" x 16ga. x 19-1/4" exh. pipe
    27 receiver tube 2" 4140 7" lg.
    28 locking lug 3/4" sq. 16ga. x 2" lg.
    29 scope mount base Picatinny rail 6" lg.
    30 base tube 3/4" sq 16ga 5-7/8" lg.
    31 bipod mount lug (match to bipod)

    * 32 (a) handle frame 1"x.100" sq. tbg. 22-3/8"
    (b) hand guard 1/2" sq. tbg.
    (c) handle 1-1/2" muffler pipe x? lg.
    (d) trigger guard 1/8x1/2" x? lg
    (e) handle frame collar 2"x.150" wall 2.8" lg.

    33,34 quick pins 1/4" dia 1-3/4" lg.
    35 bipod (purchase)

    21 * - the butt cover was an MG part, apparently molded to shape.

    23 * - plans show a cast steel muzzle brake from MG, vague description about
    making one from square tubing. I'm going to use a simple round tube
    brake like some tank cannon use. It will be a T-shaped weldment of
    the brake and the threaded mounting ring.

    32 * - plans show a cast aluminum lower, with description of a fabricated
    steel one. The plans show the weldment as a single part, so I
    split it up into a, b, c etc.

  10. #10
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    I'll bight,
    what barrel are you using ? after reading the link to the start of this build I could not find what type of barrel was used.
    muttman
    BTW the 50 griffen build was covered in SGN tresurey #3 a verry good read.

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