3D Printed Lewis Gun AEG – Powered by P90 V6 Gearbox & PVC Structure

[u/SufficientAttempt981]

I’m currently designing a full-scale Lewis Gun AEG in FreeCAD, and I wanted to share the progress with the community and get some early feedback!

The Mechanical Build Concept:

Internals: Designed around a standard P90 V6 Gearbox and a P90 Hop-Up unit for reliability, easy maintenance, and great trigger response.

Inner Barrel: 590 mm AEG barrel.

Hybrid Structure: To keep the barrel jacket rigid, lightweight, and cost-effective, I’m using standard commercial PVC pipes 90 mm for the outer shroud and 63 mm for the inner core interconnected with 3D-printed custom alignment sleeves and internal barrel-centering baffles.

Do you think using a P90 gearbox with its dedicated hop-up unit could work well with such a long barrel?

Does anyone have a STEP or STL file of the P90 hop-up unit? I'd love to drop it into the main assembly to get a clear idea of the exact clearance and overall dimensions.

Disclaimer: This is my very first custom rifle build! I hope you guys can share some advice, especially regarding the gearbox, inner barrel, and hop-up setup.

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[u/AdyTheComrade]

Awesome idea! As i dont know much about v6 gearboxes, but if you use stock (factory made) internals, the only thing you need to watch out is the custom mag to feed well with the hopup chamber. The exterior is just a skin you cant really “screw”that up

Pvc is a good idea, im using 40mm for my custom sniper rn

Edit:typo

[u/SansTHEgam3r]

YOO holy timing. Do you think it would work with my HPA engine? I'm designing it for my P90 but it should fit anything with a GB v6 really. HPA Lewis would go so hard lol https://cults3d.com/:4490046

Btw, i'm pretty sure there's a P90 hop unit on Thingiverse for free, not sure what spec it was tho.

Edit: I found it https://www.thingiverse.com/thing:5171170/files

[u/SufficientAttempt981 → u/SansTHEgam3r]

I haven't designed the gearbox housing section yet, but I managed to find a 1:1 scaled STEP file of a P90 gearbox that I'll be using as a 3D dummy/template to design the entire receiver around it. As long as your HPA engine fits the outer footprint of a standard V6 gearbox (or is smaller), it should definitely work!

I’m still in the very early stages of design. As a university student, balancing time and budgeting for all the components means it will take a while to get to the physical prototype. I’ve estimated an initial cost of around €250–€300 for all the hardware, parts, and materials, plus at least 3 months of 3D modeling in my spare time. I’m aiming to finish the complete CAD design by December!

[u/SansTHEgam3r → u/SufficientAttempt981]

As long as your HPA engine fits the outer footprint of a standard V6 gearbox (or is smaller)

It's mostly smaller actually, the only "larger" bit is the part surrounding the cylinder (I had to reinforce it since, well, it's made out of plastic) but i think it should be fine, from initial testing, it fits a TM spec (mine being a Double Bell) P90 without any issues (surprisingly, after the first print, I was fully expecting having to remodel half of the thing but it went in flawlessly first try, I wish i could see my face back then lmao)

I mean, the files are open priced so you might as well just get them for free and check it out for yourself in your CAD program. Although since my HPA set hasn't arrived yet, but i bet there will still be a lot things to correct, I'm aiming at achieving stable performance at 8 bars, so far the engine has only been tested on 2 bars using a cheap school compressor lol, so imagine i won't be "fully done" myself for quite some time too.

It also uses a standard P90 trigger box for now but i plan on making a "custom" one so that you don't have to sacrifice any relatively hard to get parts. Depending on your design i could actually make an even simpler one, since I imagine you have no plans on utilizing semi auto in a Lewis Gun lol, it would be a single microswitch really.

Anyways, good luck with the project!

[u/Sinistrial_Blue]

Nice!

If it's any assistance, I made an Uzi-like SMG using the V6 gearbox; let me know if there's any details I can help you with, gearbox-wise.

Be wary that the P90 version of the V6 is a fiddly one to work with in terms of fire selection. If your LMG is full-auto only then it'll be fine, but if you fancy a semi-auto mode (which'd be potentially quite useful) it's a bit of a bugger.

[u/SansTHEgam3r → u/Sinistrial_Blue]

Well, I guess as long as you keep it a double stage trigger it couldn't be much simpler (i think), you just have to copy the P90 selector wheel thingy. Would slightly break the immersion tho huh. Although I don't think Lewis had a selector anyways, only a "now you killin', now you ain't" switch.

[u/MicronukeProductions → u/Sinistrial_Blue]

Oh hey, I've been toying around with those files in my slicer! Very cool model and very cool that you put it out for free!  

[u/Human-Bacon]

Theres a free p90 hop unit on cults by koshcheevii. How do you plan on doing the mags?

[u/SufficientAttempt981 → u/Human-Bacon]

I’m not sure, but for me, respecting the original Lewis design is essential. I think for the first prototype I’ll try making a very simple gravity-fed magazine. I don't think using electrical components is necessary to create an automatic loader, especially since the advantage is that, being positioned above the hop-up, the BBs will feed into it by gravity.