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russc's Mag-fed 68 Special

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    russc's Mag-fed 68 Special

    Years ago I bought a literal crate of 68 specials. The Canadian dollar was at par, and I was buying stuff off eBay like crazy. In hindsight i should have bought all the $100 Autocockers instead, and now I have to do something with these Tippmanns. I figure with a 3D printer, it shouldn't be too hard to whip up a mag fed front end.

    I'll be working on the feed system first, later on I'll get into the HPA conversion side of things. The inherent modularity of a removable front end is a huge plus of working with this platform. The massive outdated reciprocating mass is a feature, not a bug...the only thing really holding 68 specials back is the liquid CO2 diet.


    The first question is what magazines...I have some random RAP4 mags kicking around, but if I'm spending the time to get this working, dealing with crappy old mags is probably not a great idea. It would be poetic to use TMC mags, but I don't have them on hand, so for now it's DAM mags.

    Next question is what orientation. I probably would go with left feed, SMG style, if it didn't require flipping the cocking rod to the passenger side. Since I'm not a southpaw I'm going to try the standard bottom feed.

    Quality of life improvements while I'm in there... I'm thinking a modernized detent, reducing the bore diameter in the breech, and potentially a larger diameter power tube which will couple with other HPA modifications. The standard 68 special slip fit barrel should work great with a printed design, but I do have an AC tap I could try. It remains to be seen whether a printed bolt will work, but I may be able to just turn the front end of the existing bolt down.

    Click image for larger version  Name:	PXL_20250125_194054745.jpg Views:	0 Size:	3.45 MB ID:	647995



    #2
    Yeah, you really should of bought the cockers. It's crazy how much leaky and dinged up stock trilogies or prostocks go for! I paid $90 for a red 2k4 prostock a few years ago! XD

    Comment


      #3
      I reverted a 68 special back to an SMG 68 using TiPX magazines instead of the plastic clips. If bulk CO2 is hard to access, the HPA conversion becomes absolutely necessary. Making yours bottom feed will be easier than a left side feed. I was working with Ty on a replacement 3D printed front with the integral magwell. We had some issue with the 3D printed plastic holding up to the impact of the gun function. I would love to see what you come up with.
      Attached Files

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      • russc

        russc

        commented
        Editing a comment
        How did your printed breeches fail?

      • COB

        COB

        commented
        Editing a comment
        The impact caused splitting along the printed seams. This may no longer be an issue with the improvements in the printers and the materials. However, seeing how badly the aluminum magazine of the original SMG 68 was destroyed by the valve, I think this will still be a concern needing to be addressed.

      #4
      Originally posted by COB View Post
      We had some issue with the 3D printed plastic holding up to the impact of the gun function. I would love to see what you come up with.
      That's a really good point...as an SMG-68 owner I know how badly these guns can beat up on anything forward of the valve. I'll have to think about that...maybe a metal insert that accepts the mounting bolts and acts as a load path for the valve impact?

      Comment


        #5
        Here's the first cut testing out some critical dimensions. Need to open up a couple bores a little larger, but importantly, the mag well opening seems to be in a good spot, and the screw spacing is correct. This is essentially just a cylinder with a rectangular base added. I'm considering turning that upper part out of aluminum, as it contains the mounting bolt threads and carries all the valve impact load, and then using a plastic spacer underneath similar to cocker to Sheridan frame adapters. The only question about that mixed material rail interface would be whether you actually get decent clamping force, or if it'll just slide around under there due to low stiffness, resulting in the two bolts taking all the cyclic loading in shear, which could work in the short term but might cause weird issues and failure later on. Could also potentially use brass and solder or alumaweld sticks...in which case I'd make the rail out of the same material and braze/solder it on.

        I'm not liking the step up/down that the bolt has to go through. Assumption was that I'd have to turn down the front 3/4 of the bolt. A printed bolt might actually work just fine here, as I don't think forces are very high what with the floppy noodle plastic cocking arm. That would let me run a single diameter bore the whole way and prevent possible hang ups as it moves through.

        That leaves developing magwell dimensions and figuring out how to attach it. Could either integrate it with the plastic rail, or bolt directly to the upper, which seems more robust from gut feel.

        Side note: The fact that Fusion's modeled 5/16-24 threads actually came out usable blew my mind...printers are so much better than they were when I first got into the hobby 12+ years ago.

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        Click image for larger version  Name:	PXL_20250126_043114085.jpg Views:	0 Size:	1.63 MB ID:	648220
        Last edited by russc; Yesterday, 01:54 AM.

        Comment


          #6
          I'm envious of everybody's CAD and 3d printing skills on here... I usually just throw stuff at a wall and see what sticks.

          Looks amazing! I think one of the Special's issues with using modern paint has been the cavernous breech so trying to maintain a consistent ID will likely help prevent feed issues.

          And God turned to Gabriel and said: “I shall create a land called Canada of outstanding natural beauty, with majestic mountains soaring with eagles, sparkling lakes abundant with bass and trout, forests full of elk and moose, and rivers stocked with salmon. I shall make the land rich in oil so the inhabitants prosper and call them Canadians, and they shall be praised as the friendliest of all people.”

          “But Lord,” asked Gabriel, “Is this not too generous to these Canadians?”

          And God replied, “Just wait and see the neighbors I shall inflict upon them."

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