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1/2 scale AR-15

Discussion in 'Rifle Country' started by MachIVshooter, Oct 6, 2014.

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  1. Field Tester

    Field Tester Member

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    How about you name it the "AR-IV"? Or "MS-IV"? :D
     
  2. MachIVshooter

    MachIVshooter Member

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    Well, as happens all too often, another appointment was a no show this afternoon. Upside is, it left me time to knock out another part. Today was receiver extension, cut from the remainder of the 7075-T6 block I used for the lower.

    This piece was kind of a bugger, made me regret my decision to go M4 instead of A2. The perfectly round A2 tube would have been a snap on the lathe. The M4 tube, OTOH, has to be cut on a rotary table due to the keyway for the adjustable stock. That meant running an extra long end mill (3/8" X 7"), which in these smaller sizes like to chatter. A lot. Result is a pretty clean finished product, but there are a couple blems from the chatter. Fortunately, they won't be visible when the stock is in place. Castle nut was cut from a spacer, haven't done the locating plate yet.

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  3. horsemen61

    horsemen61 Member

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    You do outstanding work
     
  4. MachIVshooter

    MachIVshooter Member

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    Gas key and take down pins done.

    Gas key was easy, tapping the insanely hard steel of the carrier not so much. Multiple drill bits and two taps later, it's secured and staked with a pair of #2-56 screws:

    IMG_1203_zpsef99c280.jpg

    Pins were done by reprofiling some long #6-32 screws. Cutting the slots was a challenge, but they were otherwise very easy. The detent pins and springs I sourced from a local jeweler in the form of wrist watch spring bars. Just disassembled a couple of 1.5mm spring bars, stole the 1.0mm pins and springs.

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  5. cosh

    cosh Member

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    Wow - gunsmith meets watchmaker. I hope it runs like a Swiss watch when you get it done. [emoji39]
     
  6. barnbwt

    barnbwt member

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    I love that you staked the gas key screws :D. #2's, that's some pretty small stuff, right there. I can't believe you were able to tap pre-hard steel for that! :eek:

    Have you thought about how you'll do the stocks when the time comes? Farming them out to one of the online SLA 3D printers (not FDM) would get you some insanely accurate 1/2 repros that look and feel like the real deal (probably just about as strong per square inch, too). So long as you aren't printing receivers, none of the outfits should have problems printing "toy model" AR parts ;) (some of them are gun-shy and don't like making usable parts)

    TCB
     
  7. MachIVshooter

    MachIVshooter Member

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    Got the charging handle done late last night. That ended up being a lot more work than anticipated, with a lot of careful fitting to get everything sliding smoothly. about 6 hours all in. I did goof a little and overran my numbers where the rear should be profiled to fit the horizontal cut in the receiver, but it will not affect function and is barely noticeable. After what I went through, I'm not inclined to redo the thing right now. The handle is also a tad thinner than scale; I didn't want to cut the receiver extension housing down any further, and a 4140 steel handle can be trimmer than an aluminum one.

    The handle is cut from 4140 chromoly stock, the latch is spring steel, using a 0.041" drill bit for a pin and a 0.055" coil spring. I only blued the rear of it, as the bluing will wear off wherever it contacts the receiver anyway.

    IMG_1208_zps4d3fbbfa.jpg

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    That's a possibility, but I'm confident I can machine it from the black ABS I have on hand. Kinda be cheating if I contract out something I can do, ya know? I'm already probably gonna have to bite the bullet on hammer and trigger springs, pay a spring maker to duplicate production springs in 1/2 scale. No matter what stock I start with, I just can't seem to get appropriate form and tension bending them myself.
     
  8. Ar180shooter

    Ar180shooter Member

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    WAY too cool!
    Awesome work. :D
     
  9. MachIVshooter

    MachIVshooter Member

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    Today was productive. Ran into a snag when I couldn't find my #3-56 die, but the trip across town to A&A Tradin' post (shout out to those guys, BTW. A REAL hardware store with actual hardware and staff that knows hardware) proved fruitful, as I was able to find my 15/32"x6" buffer springs.

    Anyway, got the buffer detent, buffer, magazine catch and barrel nut done today. Not sure if I'm gonna run this nut or redo it, though; it was a 5/8x1" steel spacer, so there will only be a 1/16" shoulder for the barrel flange. If I use it, I'll put a cut across the face for a spanner wrench, and the hand guards will be one piece that slide over the barrel before the front sight is attached. I also still need to stick a piece of acetyl in the back of the buffer, but that's not a big deal. Haven't decided if I'll put the triangle cuts on the front of it, either; larger bearing surface without them.

    I did have to make the buffer detent pin twice; shot it across the garage, and a 1/8"x5/16" piece of steel launched across my shop is a gonner. I;d have spent more time looking than redoing.

    The buffer springs I got may need to be clipped, too. As of right now, if I release the charging handle with the bolt fully rear, it will strip a cartridge from the magazine and spit it out the open hole in the front with enough velocity to launch the whole cartridge about 20 feet with the gun is level at my chest height. If it misfeeds with a barrel in place, I guarantee it'll absolutely crush the cartridge, possibly even detonate it.

    Anywho:

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    And one with a round sitting on the bolt face just for fun:

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  10. MachIVshooter

    MachIVshooter Member

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    Oh yeah-it weighs in right now at 10.2 ounces with a fully loaded mag. Lol. I don't think this thing will top 1.5 pounds when done.
     
  11. ArchAngelCD

    ArchAngelCD Member

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    Outstanding work Sir, thanks for sharing it all with us!
     
  12. Mp7

    Mp7 Member

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    awesome shizzle is awesome.

    (needs a loooong collapsible stock :) )
     
  13. iwilc2

    iwilc2 Member

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    Simply amazing work Sir







    Len
     
  14. Rubber_Duck

    Rubber_Duck Member

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    Amazing. This is one of the coolest things I've ever seen. I look forward to seeing more.:)
     
  15. coctailer

    coctailer Member

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    Subscribed:cool:
     
  16. MachIVshooter

    MachIVshooter Member

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    I may redo it later on account of a couple errors that resulted in minor blems, but stock ver 1.0 is made, though I still have to make the lever and pin assembly.

    This is the photograph I am using in my letter to ATF requesting pistol classification for the firearm, which is going in the mail today:

    AR-75ATFpic_zps3fca88bf.jpg
     
  17. g5m

    g5m Member

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    Wonderful work!
     
  18. Doc7

    Doc7 Member

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    This is really nice. I like the collapsible stock idea allowing it to be shot as a rifle (if legal)
     
  19. Slimdog

    Slimdog Member

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    Simply amazing. Strong, strong work!
     
  20. MachIVshooter

    MachIVshooter Member

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    It would be pretty much physically impossible for any human being with normal physiology to shoot as a rifle with the scale stock. At full extension, the rear of the stock is 5.2" from the back of the receiver; try holding a pistol 5" away from your shoulder and looking down the sights. Wrists and necks just don't bend that far.

    That is the premise on which I am asking ATF FTB to declare this thing a pistol even with the scale stock; the stock is functionally useless, being that there is even less LOP on this than what's left of the "stock" on the commercial title I "mares leg" pistols:

    web_henry_mares_leg.jpg
     
  21. Gaiudo

    Gaiudo Member

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    Tag to watch this develop. Fantastic stuff.
     
  22. WestKentucky

    WestKentucky Member

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    Coming together nicely and quickly for a project as intense as this is. Good work.
     
  23. Panzerschwein

    Panzerschwein member

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    Incredible!

    Looks VERY nice! The production model would make a great first rifle for the unborn fetus! :D
     
  24. chicharrones

    chicharrones needs more ammo

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    Still watching every time a post is made in this thread. The "Wow" factor continues. :cool:
     
  25. jerkface11

    jerkface11 Member

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    It didn't click how small the thing is until I saw it next to the Glock.
     
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