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Old 04-07-2018, 11:08 AM   #1 (permalink)
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SMG 68 Mag Repair

Howdy!

Has anyone repaired, or fabricated, SMG 68 Mags? I have one with the typical collapsing end that jams up clips. Seems like the easiest fix would be to flip the mag around and mill the other end, until that end eventually collapses. I usually prefer not to make non-reversible modifications to vintage equipment though.

Last edited by RuleOfSines; 04-07-2018 at 11:13 AM.
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Old 04-07-2018, 11:33 AM   #2 (permalink)
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you could just sell it to me!!
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Old 04-07-2018, 12:08 PM   #3 (permalink)
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you could just sell it to me!!
But then I wouldn't have it anymore, and that just won't do!
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Old 04-07-2018, 12:44 PM   #4 (permalink)
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So the mag is made from extruded aluminum so getting that is not likely. But maybe someone could Print it on a 3d printer, no reason that I can think of why that wouldn't work. Then you can save your mag.
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Old 04-07-2018, 01:11 PM   #5 (permalink)
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The mag actually sees a pretty sizable impact, the front cup seal is braced against it, and gets shocked from the hammer with each shot. I could print a part, but I don't think it would survive long in that scenario.

Bacci has an article from a couple years ago about the issue, https://www.baccipaintball.com/oldne...prone-magazine

I was thinking of maybe a steel adapter that slides into that part, that accepts a separate magazine.

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Old 04-07-2018, 01:13 PM   #6 (permalink)
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That would be cool
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Old 04-08-2018, 03:46 PM   #7 (permalink)
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The smg-60 magazine was steel. Have you considered using steel tube stock and milling to match the aluminum original.
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Old 04-09-2018, 09:09 PM   #8 (permalink)
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The smg-60 magazine was steel. Have you considered using steel tube stock and milling to match the aluminum original.
There are some options there, but the SMG 68 mag is an oddly shaped extrusion. It has paths to clear the spring, as well as the clip pawl mechanism. For whatever reason they moved the advancing mechanism from the marker body to the magazine body.
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Old 04-10-2018, 12:51 PM   #9 (permalink)
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I think the easiest way to make an adapter would be:

1. EDM or Waterjet-cut a blank out of steel to get the important extruded profile. This would extend across the entire breech.
2. File or broach to remove the 1-2 degree draft angle that you get from such a deep cut if waterjetting...unless tolerances allow it to stay.
3. It would then need the various holes to be drilled, but that part's easy and can be done on a manual machine.
4. Finally, weld a plate on to the end to cantilever a magazine just like the SMG-60.

In fact, am I remembering correctly that SMG-68 clips fit into SMG-60 magazines? If that's the case it might be possible to simply make the adapter use existing mags. Otherwise you'd use whatever square tubing that's available and either weld it permanently to the adapter or make your own SMG-60 style mag.

If someone wants to model the blank as a solidworks or DXF file, I have occasional access to a waterjet. Between finals and Baja SAE I don't really have time to design anything, but I could probably do the cutting. If someone has EDM access though, that's the way to go for sure.

Also I would expect the adapter would eventually fail as well...I'm just spitballing but I would assume it's a pretty high-stress part and might end up above steel's endurance limit. but it would last much longer than the aluminum. the profile you've got inside these things is not ideal. You could probably estimate fatigue life or check against steel's endurance limit if you consider just the one side of the mag to be a beam loaded by a single point load.
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Last edited by russc; 04-10-2018 at 06:57 PM.
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Old 04-11-2018, 10:43 AM   #10 (permalink)
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O would it be so simple. The problem is that on the SMG 68, the index pawl was moved from the body on the SMG 60, to the magazine. Any replacement magazine must have this added to a stock square tube.
I Did this by reconfiguring a 68 Special front end and mounting the feed index pawl there. I used stock 1 inch square aluminum tube for the magazine.
I had a SMG 68 and in addition to the compression problem, the indexer pin kept falling out. It was a bad choice of material for the magazine.
My current thinking is to make new magazine fed front ends and modify the valve and power tube for SHP hpa
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