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Old 06-29-2018, 03:48 PM   #1 (permalink)
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russc's summer project: another mag-fed mag

As some of you may have heard, I'm in school for mechanical engineering. I landed a sweet summer gig that offers extended shop hours. We've got access to cheap waterjet cutting, free use of a Tormach CNC, and I've got a student version of HSM Ultimate. I've got two months left, so my goal is to design and manufacture an idea that I've had kicking around for a while, and Ghost Flanker has proven feasible with his MFG.

I'll just get this out of the way...does anyone here have HSM experience? I'm just teaching myself as I go, and could definitely use a second opinion on my CAM before I load the machine.

For some background, this idea goes all the way back to 2012 when I was working with Avratech. I actually emailed Tom Kaye this picture, and asked him about making an extended Automag bolt to space out the magwell:

Right now I'm planning on the following features:
  • Custom autococker threaded aluminum body
  • Custom rail
  • Custom frame based on AGD CF dimensions (Gotta have SP wood grips)
  • CNC'ed, swappable magwell (Designing around TPX right now, but I'd like to use DAM as well)

For the body, I'd like to avoid doing long, high-aspect ratio boring, and squaring up multiple operations in a 4-jaw lathe chuck. For this reason I'm ditching the combined body/rail idea, and considering doing a short center section for the barrel threads and breech. I'll turn a thicker steel spacer instead of using the circlip that AGD used on ULE bodies, which requires some finicky grooves. The final form will be something like these CF bodies, but with an aluminum or stainless rear tube:

Here's the base modeling so far. Still need to separate the body into front and rear sections, and obviously I'm ditching the idea of an AR-patterned thread-mount up front. In 2012 that was novel, now AR clone mag fed guns are everywhere and I'd rather just keep things minimalist.

Frame spacing and attachment is a problem, so I think I'm going to have to do something totally proprietary to get the front attachment point on there. The frame is going to be totally custom, so options are wide open. For manufacturing, I think I might try waterjetting a blank and then doing the radius cuts with it bolted down onto a fixture.

Tippmann-style push-pins front and rear would be really easy to work with, and would let me quick-strip to get access to the valve thumbscrew. That said, I'm a bit wary of how much wobble that would introduce, so I might go with just a front push-pin, and a threaded rear mount.

I've also got the FSR profile cut into the rail right now, but I'm going to flatten that whole section out as close to the body as possible. That will allow me to play with the magazine interface dimensions, instead of getting locked in to one offset height.

Last edited by russc; 06-29-2018 at 03:55 PM.
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Old 06-29-2018, 06:59 PM   #2 (permalink)
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Old 06-29-2018, 07:44 PM   #3 (permalink)
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Old 06-29-2018, 11:16 PM   #5 (permalink)
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Old 06-30-2018, 01:23 PM   #6 (permalink)
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Old 06-30-2018, 02:14 PM   #7 (permalink)
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Works to simulate code from Fusion360, which is based on the HSM software. Should be able to use that for simulation.
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Old 07-01-2018, 02:08 AM   #8 (permalink)
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I’ve actually started something similar.... what I’ve decided to do was go with an 80% lower that I will machine to my finished specs. That way I can integrate my frame and Magwell. I love your body idea. I was debating if I wanted to turn an extension for the body and press/braze it all together to get the length I want/need.. of course this road would also require a custom bolt.... either way not too difficult
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Old 07-12-2018, 03:21 AM   #9 (permalink)
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Torn on slider vs. hinge can see the frame attachment thought process with those push-pin bosses on the rail. Not 100% sold on those but it would be an easy solution to that front mounting problem, and would make quick stripping nice.

I should be able to waterjet the majority of the frame profile and then it'll be 3 really simple setups to get the fillets and trigger slot cut. Gonna have to incorporate some kind of fixturing in there...some dowel pins to align it to a plate, and big clearance holes for bolts? Also planning on 3D printing the frame before I do anything drastic, because it's SP wood grips on there or bust.

Last edited by russc; 07-12-2018 at 03:29 AM.
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Old 07-12-2018, 09:48 AM   #10 (permalink)
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Getting that frame attachment pushed back will be interesting as usual.

The Ruger MarkII (+) has a tongue and groove on the front and a pin in back. That might be an option. Since it is magfed, you also have the option of making the rail deeper around the sear area.

Wings on the frame would might mess up the water jet cutter plans...

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