3D Printing Glock Mag Extension Guide

A magazine extension does three jobs at once. It adds round capacity, it keeps the magazine spring under enough preload to lift the last round, and it holds the magazine seated in the frame under recoil. A part that only does the first job will fail at the range.

The extension body is a tube with a floor plate interface at one end and a spring seat at the other. On a printed part, the floor plate interface is where tolerance stacks up fastest. FDM printers hold roughly ±0.2 to ±0.4 mm on a well-tuned machine; the frame's magazine well and catch are far tighter than that.

Printed extensions work best as a low-volume, personal-fit part. If you need a batch of 50 identical units that drop into any G17, the printing step becomes a pattern step and the final part should be machined or molded.

One more thing worth saying early. The magazine spring is the part that decides whether your extension feeds reliably. A longer tube needs a longer spring, or a spacer that keeps the original spring in its working range. A printed extension with a stock spring and no spacer will not lift the last few rounds fast enough.

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  CapacityAdded length times tube cross-section, minus the spring coil stack.
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  PreloadSpring force at the top round; too low and the last round hangs.
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  RetentionThe catch notch must survive repeated insertion and drop.

PLA+ is the easiest to print and the cheapest to iterate, but it creeps under spring load and softens in a hot car. Use it for fit checks only. PETG is tougher and slightly more flexible, which helps the catch notch, but it strings and needs a dialed-in profile.

PA-CF (carbon fiber nylon) is the usual pick for a functional printed extension. It is stiff, has good fatigue resistance, and holds a thread well. It also absorbs moisture, so dry it and print from a dry box. Annealed PA-CF can take the spring load of a 10-round extension without visible deformation.

For parts that see real duty use, print in PA-CF or print a pattern and machine the body in 6061-T6 or 7075. Aluminum weighs more than plastic but does not creep, does not care about heat, and can be hardcoat anodized for wear at the catch.

Do not use PLA for anything that holds a loaded magazine. It will take a set and the floor plate will stop seating.

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  PLA+Fit checks and display parts only; creeps under load.
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  PETGTough and cheap; watch stringing and layer adhesion.
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  PA-CFBest printed option; dry before printing, anneal after.
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  6061-T6 / 7075Machined or metal-printed body; no creep, hardcoat anodized.

Wall thickness is a balance. Thin walls save weight and let the magazine drop free; thick walls resist the spring pushing the tube outward. For FDM in PA-CF, 2.5 to 3.0 mm is a good starting point for the side walls, with 4 to 5 perimeters. Add a vertical rib on the front and back faces if the extension is longer than about 40 mm.

The top of the extension meets the original magazine tube. If you cut the original tube, the joint has to be square within 0.1 mm or the follower will tilt and jam. Most builders keep the original tube and clamp a sleeve over it instead, which removes that cut from the equation.

Feed lip geometry is the one feature you should copy from a working magazine, not redesign. Measure the original with a caliper, or better, section a magazine and measure the lip angle. Reprint the lip region in 0.1 mm layers so the surface is smooth enough for the follower to slide.

Spring seat depth sets preload. A simple rule: the seat should compress the spring by about 15 to 20 percent of its free length when the magazine is fully loaded. If you cannot source a longer spring, print a spacer that sits between the spring and the floor plate. Keep the spacer under 20 mm so it does not buckle.

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  Side walls2.5–3.0 mm in PA-CF with 4–5 perimeters.
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  JointSleeve over the stock tube; avoid cutting if you can.
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  LipsCopy the original geometry; print in 0.1 mm layers.
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  Spring seatCompress spring 15–20% of free length when loaded.

The practical workflow is the same one we use for other small mechanical parts. Print two or three versions in PLA+ to check the fit in your own frame, then move to PA-CF or a machined body once the geometry is settled. A printed prototype costs almost nothing and tells you more than any simulation.

When the design is fixed and you need repeatable parts, we machine the body from 6061-T6 or 7075 on 3-axis and 4-axis mills, with the internal tube bored or milled from both ends. For a part like this, ±0.005 mm is available on critical features, but the magazine well and the catch notch are the features that matter; a loose cosmetic surface is fine.

If the geometry has internal ribs or a lattice that cannot be reached by a cutter, metal additive plus finish machining is an option. We print the near-net shape, then machine the joint face, the catch notch and the spring seat. That keeps the internal features and the tight fits in the same part.

Surface finishing matters here more than on most parts. Hardcoat anodizing on aluminum raises surface hardness at the catch and the feed lips, and bead blasting removes the layer lines if you are keeping a printed body. Both options are in our normal finishing list.

Quantities are flexible. One prototype or a run of 10,000+ parts, with no minimum order quantity. Uploads stay confidential and we sign an NDA on request.

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  PrototypePLA+ print, fit in your frame, iterate geometry.
• 2
  Small runPA-CF or MJF for 10–200 uniform parts.
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  ProductionCNC 6061-T6 / 7075, hardcoat anodized.
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  Complex internalsMetal AM near-net shape plus finish machining.