DIY Sig P938 Rail & 8rd Magazine

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My EDC is a Sig Sauer P938. I like the size and with the factory 7rd extended magazine it feels like a compact.

However there is room for improvement. Sig Sauer has a trigger guard laser that you can buy and attach to the P238 or P938. It works for both guns.

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I am not a fan of lasers as much as I am a fan of flashlights. So I got a broken laser unit to make into a rail for a light.  I sent the broken Sig laser to my friend Alex to reverse engineer and draw in 3D. I told him redraw it and remove the laser portion but replace it with a picatinny rail. Here is the drawing of that rail.

P938 rail

 

He drew it up for me and I printed it through Shapeways.

For the light I went with a Viridian C5L as that was the smallest rail mounted green laser with white light that I could find.

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Next modification was due to playing with a Sig Sauer P290 Liberty Edition. It comes with an extended magazine that holds eight rounds. Looking at the magazine, it has similar dimensions as the P938 magazine. I took one and shoved it into the P938 and it fit.

You can see the factory P938 7 round magazine next to the P290 8 round magazine.

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The only issue was the magazine notch was not the same. I bought a P290 extended magazine and cut a new mag notch with a dremel. Not perfect looking but completely functional. It will load and chamber rounds. Look at the magazine on the right, the two small square holes is the factory notches for the P290 and the cut above is for the P938.

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The P290 magazine is not that much longer than the P938 magazine and you can hold one extra round. Now I can carry 8+1 in my Sig P938.

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The P290 extended magazine has a large pinky extension. I had to chop the top of the plastic extension off a bit for the magazine to seat properly. Otherwise the extension would hit the bottom of the pistol grip before seating.

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The larger P290 extension makes for a more comfortable grip.

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You do not have to use the P290 extension if you so desire and the magazine body acts as a pinky extension.

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Below is a factory 7 round P938 magazine with pinky extension removed.DSC_0150 DSC_0149

If you so desire, you can use the P938 pinky extension and use it on the P290 magazine. Since the floor plates of the two magazines are different, the P938 extension does not protrude past the bottom of the P290 magazine.

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Of course all of this does not matter if I cannot carry it. So my friend at Dark Star Gear made me a custom kydex IWB holster for this setup.

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Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

Any questions please email him at nicholas.c@staff.thefirearmblog.com


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  • Iggy

    While the basic idea is sound, it looks a little kludgy, for something you’re relying on for self defense. While it doesn’t effect anything essential for basic purpose, the light mount looks like it’s about to spontaneously fall apart if I keep looking at it too hard, but obviously it’s stronger than it looks if you’re trusting it, what’s the material?

    • Nicholas C

      I don’t know the exact material but it is their White Strong Flexible material. It is as advertised. Not brittle and strong. It isn’t ABS. I believe it is laser sintered. It is not the extruded monofilament abs like makerbot.

      • Jared Vynn

        How was the service and cost of shapeways?

        • Budogunner

          My fiance and I have matching custom, silver engagement rings from Shapeways. For what we got, the pricing was good. Especially when compared to jewelry store prices.

          If you don’t have a printer at home, they are a reputable choice. In my case I have a rep-rap style printer but the lost PLA casting process to produce metal results was intimidating, so they have value even for those who do print at home.

        • Nicholas C

          The rail is two pieces. Left and right. It cost me like $5 per side. In the past they have been fine but I do not order that much from them. When i got the rail they sent me two of the same side. So i emailed them and they rushed the part to me. It was a mistake on their end. I checked my order and my file to make sure I didnt upload the same file twice and call it different things.

          Turn around time is a bit slow. It is like 2 weeks from when you order to when it arrives. Some other times are slower.

  • Jim

    Most 3d printers work in abs plastic. It is surprisingly strong, even if it is not a solid infill. If this is higher than 30% infill, I’d say it would follow it’s job.

    • Nicholas C

      This isn’t ABS. It is their White Strong Flexible material. I had done custom Glock 21 speed plates made out of this stuff. Going strong for three years.

      • FYI – That “White Strong” material is Nylon

  • TheNotoriousIUD

    Damn, now that is some nice work. Good job.

  • DancesWithGlock

    The light/laser looks slightly angled down compared to the bore. Was there still enough adjustment zero it?

    • Nicholas C

      Yep it is zeroed at 15 feet.

  • Nicholas C

    Intersting. No I did not know that. Thanks!. However looking at it, it uses those small batteries. This uses a CR2 battery and it is a green laser. Green is better LOL But that is cool about the Streamlight light/laser combo. I will look into it.

  • TheNotoriousIUD

    How much for one that fits a P238?
    In black.

  • Mickey R

    Oooooh, that’s nice! I need one of these for my P938.

  • thedonn007

    Thanks for the tip on shapeways. I have just started looking into buying a 3D printer for making prototypes of firearms accessories, but shapeways might be the way to go for now.

    • Nicholas C

      Yep especially for one off prototypes. Also, very important, don’t label it anything gun related. Or have obvious gun shaped objects. It is stupid but they are anti-gun.

      • thedonn007

        Thanks, I will be sure to call them Picatinny rail adapters for things like lights / lasers and cameras.

        • Nicholas C

          I would call them keyfob doohicky LOL

        • JamesRPatrick

          “Picatinny” is distinctively gun.

        • Zachary marrs

          Device/accessory interface adapter.

          Picatinny is too obvious

          • Spikey DaPikey

            Fast Adaptive Rail Things 😉

  • gunsandrockets

    Well done! What is the final weight of your modified and and fully loaded P938?

  • Prime Client

    Wouldn’t it be simpler to buy the right gun to start with? Is eight rounds that hard to find?

    • valorius

      Ah yes, “wouldn’t it be simpler,” the driver of innovation the world over.

  • n0fry

    Is there anyway we can purchase the blueprint file for the rail attachment?

  • Dickie

    Off topic, but realted to Sig Sauer. Anyone know a release date for the P220Legion??? It was mention in a post last month and have yet to find any info of it elsewhere online.

  • valorius

    Kewl