Introduction: Printable Airsoft Submachine Gun

Picture of Printable Airsoft Submachine Gun

After designing my first 3D printable airsoft gun, a few people have been requesting a smaller one that they can print at home. So here it is!
All parts are small enough to fit comfortably in a 120x120x120mm print volume, there are fewer non-printed parts, and it has more features. The gun won't be as powerful as the previous design due to it's smaller size, but on 0.12g bb's it'll shoot 25-30m.

STL's can be downloaded as a zip below.
You'll also notice an animation. If you're not so confident you can follow the instructions here, take a look at the animation. It is an exploded view disassembly of the gun, so you can pause and check you've made yours correctly.

Here is a list of the non-printable parts you'll need:
3 x M4x25mm* countersunk bolts
1 x M4x25mm buttonhead bolt
2 x M4 nut
1 x M4x38mm countersunk bolt
1 x rubber band between 50mm-100mm long (measured unstretched flat)
3 x 5-6mm OD* 20mm long pen springs (any pen spring will do)
1 x 5-6mm OD 60mm long pen spring
7 x 2mm OD 20mm (or longer) nails
1 x 2mm OD 60mm long flat head nail
2 x 1.5mm OD 20mm (or longer) nails
1 x Bike Pump*
1 x 190mm airsoft barrel & hop up bucking
1 x 1m of aluminium flat bar (12mm x 3mm cross section)
1 x 700g (or more) reel of ABS printer filament (black recommended)
1 x 100mm long bb pistol spring, or any spring of your choice (15mm OD)

And here are the tools you need:
► 3D Printer with 120mm cubed volume
► Pliers/side cutters (for cutting nails)
► Support removal tools
► Sand paper
► Phillips head screwdriver

*M4x25 means 4mm diameter (outside of thread) and 25mm long
*OD stands for 'outer diameter'

Step 1: Features

Picture of Features

Before you start building, it's good to have an idea of what the final product can do.

Here are some features:

  • Foldable and removable stock
  • Working safety
  • Twist to remove barrel for quick unjamming
  • Easy access adjustable hop up
  • Folding foregrip
  • 13 round mag
  • Quick change spring
  • Removable backplate- piston access
  • Single-pin field strip
  • Anticlockwise thread on over-barrel silencer
  • Weaver rails, will fit standard attachments

For all the engineers out there, here's a brief overview of the design:

The focus of this design project was on assembly. The entire gun can be broken down into it's basic components with the removal of only 2 pins. This is possible because of sequentially constrained parts, where a pin holds one part in place, which in turn holds another part in place, and so on.
It's an original design, I used Solidworks to CAD it up, and an UP Plus 2 to print it. One of the challenges was to design all the parts to fit within a 120mm cube print volume. This required major parts like the receiver to be split into 3 parts, creating the need for mechanical connections between these parts. So I had a lot of fun finding creative ways of assembling these components without increasing the use of non-printed fixtures.
The design process (concepts through to CAD) was spread over about 6 months due to university and work, but overall took about 3 weeks of full time work to complete.

Step 2: Printing and Collecting Parts

Picture of Printing and Collecting Parts

Get a hold of all those parts I mentioned on the first page while you're printing. STL's can be downloaded from the first page if you missed that.

You'll notice I have a reflex sight there as well, this is optional as the gun is printed with sights.

I harvested my springs from dead BIC pens, but any pen springs will do as they are all similar sizes. Cut them to suitable sizes when you come to assembling the parts.

The piston spring came from an old bb gun, but you can find similar springs at a local hardware store if you don't have a spring lying around.

Cut the cylinder of the bike pump to 50mm long and deburr the edges. Take the o-ring off the piston, and try and keep the grease so you don't need to re-lube your piston.

Step 3: Assembly- Folding Foregrip

Picture of Assembly- Folding Foregrip

Pictures are pretty self explanatory for the next few sections, but let me know if you have any questions. One thing I will say though, keep the sand paper handy, you'll need it to get these parts moving smoothly.

Step 4: Assembly- Hop Up

Picture of Assembly- Hop Up

This hop up unit is a little tricky to assemble, but again, the pictures do a better job than me explaining it.

Step 5: Assembly- Trigger Box

Picture of Assembly- Trigger Box

The trigger box is split into two parts, one holds the sear, the other holds the trigger. A link is inserted into the receiver later on that will connect the two.

You'll notice there are no photo instructions for the trigger side of the trigger box, but it is pretty simple to figure out. Check the animation if you're stuck, and if you still can't get it, just leave a comment and I'll see if I can help.

Step 6: Assembly- Mag

Picture of Assembly- Mag

In the previous gun, a few people had trouble finding an old bb gun mag for the spring. So instead of a spring this time, I designed the mag to use a rubber band. Use some common sense here to find the right length of rubber band to cut, the ram should still have tension on it at the top (when there are no bb's in the mag). You will need to use some sand paper to get it sliding smoothly.
To thread the rubber band through the body of the mag, I use a piece of wire.
The nail used for the pulley wheel here has a 1.5mm diameter.

Step 7: Assembly- Stock

Picture of Assembly- Stock

Making the stock is optional, but I think it looks cool.

The aluminium flat bar will need to be bent into shape. You can make it any length you want, mine is 260mm from end to end. So first cut a length of bar to (2xLength)+44mm, where Length is roughly the distance of the stock from end to end, and 44mm is the internal width. Mark off the centre and measure 22mm either side as your fold lines. Place the bar in a vice or grab it with the pliers at your bend lines and bend a touch over 90deg so the ends point inward when you're done. This will help them clamp onto the receiver.

Step 8: Assembly- Barrel

Picture of Assembly- Barrel

If your barrel is a little shorter than 190mm that's fine, it will still fit, but over 190mm will stick out the end of the outer barrel!

My hop up bucking was a cheap fake madbull, but most are standard sizes so you can get any brand that you want.

You can print a flash hider as well if you don't like the silencer, both have anitclockwise thread and you can change them out easily.

Step 9: Assembly- Receiver

Picture of Assembly- Receiver

Pics should show everything, except the assembly of the bolt and rails.
Once you're cut the cylinder to 50mm and deburred the edges, use some epoxy to glue the cylinder head into one end. Cut a 1.5mm diameter nail and pin the fin into the cylinder head as per the picture. The 60mm long flathead nail should clip straight into the top of the clinder head.
The rails on the receiver are simply acetone fused in place. However, if you have some spare epoxy, you may wish to do this at the same time.

Step 10: Assembly- Putting It All Together

Picture of Assembly- Putting It All Together

Now for the fun part, putting all these sub-assemblies together! Follow the pics, should be pretty easy, but do let me know if there are any details that I have missed.

Step 11: Painting

Picture of Painting

I used a slow cooker with some acetone to smooth the surface of the parts. Make sure they fit together well before you do this however, or you'll need to sand them again and defeat the purpose of the acetone.

I spray painted my gun black (with white primer), but the paint had a slightly sticky feel to it, causing some parts to grip tightly. I would recommend printing in the colour you want your gun to be so you avoid painting. However, I was able to sand the edges to give a worn look. Again, up to you!

Hope you enjoy this building this gun if you choose to, make sure you use it responsibly as always. Take a look at the parts understand how they work together, I hope it will inspire you to get into some CAD and start designing!


simonres (author)2017-07-18

how much filament do you need to print this?

NathanL77 (author)2016-12-29

Anybody have any tips for warping? I would have had both of Engineer's guns made by now if there weren't any warping :)

Vrael19 (author)2015-09-22

@Engineer777 I am looking at purchasing my first 3D printer and have been doing a ton of research on what is out there and affordable. Could you give some info on the printer you use and/or other models that you think could take on builds such as this without spending ridiculous amounts of money? I'm a student with limited funds but im finding it hard to resist a new hobby like this. Thanks for any info you can provide, your designs look awesome and i cant wait to try them out!

DejaVuP (author)Vrael192016-12-20

If I may join in the conversation, I found that the Flashforge Finder 3D printer is Affordable and is very reliable I find. (look at other reviews for confirmation ;3)

Also VERY important thing to note: ONLY PRINTS IN PLA.

(PLA is cheaper than ABS but weaker, it also seems to be easier to print in and less likely to fail)

Engineer777 (author)Vrael192015-09-24

Hey man,

Awesome! Don't resist the hobby haha, can lead into an awesome career.

Yeah so the printer you get will really depend on what you want to be printing. You won't be able to print a couple of the big parts from my rifle design on a standard desktop printer- even if the printbed is big enough. Parts just warp when they get big, you can't really go beyond about 150x150mm on an 'open bed' printer, i.e. one without a heated chamber. So just be aware that a 200x200mm printbed doesn't mean you can print a 200x200mm part.
But hey, that's why I designed the smaller submachine gun!

I use an 'UP! Plus 2', and it just works every time, so reliable. Means I can just hit the print button and it works, rather than spending an extra hour scraping off failed prints before getting it to work. So if you are thinking along the same lines, go for an UP, maybe the UP Mini would suit your budget more:

You'll probably want to check out suppliers in your country though, postage would kill.

Just a few general pointers:
- Dual nozzle is a gimmick, just use spraypaint. Plus it makes the printhead bulky and reduces the quality of your prints.
- Makerbot is unreliable, can match an UP for print quality though.
- Don't be sucked in by the low prices of kitset printers, you can spend more of your time trying to fix your printer than actually printing!
- Stay away from printers with proprietary cartridges so that you can buy cheap plastic elsewhere.

Good luck!

Northbadge. (author)2015-11-15

Could you update the bike pump's link? The one you have wrote is no longer available

Engineer777 (author)Northbadge.2015-11-15

Here's a link below, will update the instructable when my internet decides to work.

Thanks for letting me know!

BostonS (author)Engineer7772016-01-22

Does it have to be that in particular or can I get one from my local Kmart cheers

DejaVuP (author)BostonS2016-12-20

any small bike pump *should* work

EricC261 (author)2016-11-25

the article expired.

is this pump fine?

Laurex2002 (author)2016-10-10

why do you need a bike pump?

HeisenK (author)2016-09-06

Which software should i use to open the files?

Engineer777 (author)HeisenK2016-09-06

Hi there, the .stl files are for 3D printing, so use your printer software for those, and the .sldprt files are CAD files which can be opened and edited in Solidworks.

HeisenK (author)Engineer7772016-09-06

Ok thanks. Btw you really should make a pistol when you have time

OskarF1 (author)2016-07-12

engineer 777 would you be making a pistol variant anytime soon for example a walther

Engineer777 (author)OskarF12016-07-12

Hey man, unfortunately not as I don't have the time

Buck10 (author)2016-07-06

Is this on a 3d printer also what is the scale size EG(4x5) please replie thanks

Engineer777 (author)Buck102016-07-06

Hey, yep this design is for 3D printing. Not sure what you mean by scale size, but if you're talking about the largest part size, it would be around 200x80x80mm

Buck10 (author)Engineer7772016-07-06

Thanks exactly what i ment love your work

Engineer777 (author)Buck102016-07-06

Ah sorry! I gave the largest part size for my other gun. For this one, the biggest part is actually under 130x80x80mm

GeoffF7 made it! (author)2016-05-26

Engineer777 this is an amazing design, thanks so much for sharing it. I have made the gun and after each section came off the printer and I assembled it I was continually amazed at how well it was designed. It is firing nicely however I do get one slight issue associated with the fin and the action of dragging the new BB up the rail to the barrel. It tends to "pop" out of the mag head with a bit of force and bounces around in the chamber a bit (with more force when the mag is full and the rubber band is tighter). Usually it locates itself OK but sometimes it drops to the left or right of the ramp and then gets jammed against the outer barrel/barrel housing assembly when the piston head comes forward to complete the loading process. Just wondering if you have encountered this issue and can suggest any type of workaround. I can see no obvious one tinkering with the model.

Engineer777 (author)GeoffF72016-05-26

Awesome man! Glad you appreciate the design.

I didn't have this problem, but I imaging it is because of your rubber band tension (as you mentioned). The mag is designed with a tiny ridge in front of the bb to stop it popping out on its own. So when the fin passes over top, the bb has to get under the ridge before it pops out onto the track. The first thing I'd try is a looser rubber band, but if that fails, see if you can sand down that ridge in the mag. Also make sure there are no lumps on the track itself which migth contribute to the dislodging.
Failing that, try pushing the bolt forward really fast haha.

I'd be interested to see how you get on!
Thanks for the photo and screenshot too

GeoffF7 made it! (author)Engineer7772016-05-26

Thanks for the reply! Yeah I set the rubber band to basically min allowable tension as a first move - so it barley has enough force to load the final BB.

The mag is def OK - functions as you say, holds the BB for the fin return. It is where the channel opens up coming onto the lip of the front receiver and the ramp (see pic). From playing with it without the barrel in it seems like the force of the fin return "pool cues" it up the ramp, where it would then hit the end of the barrel and bounce off to the side - all before the piston head has located itself flush on the barrel end. My return action does slow towards the end actually when the spring is armed. It is fine when the spring is out, very fast and smooth. Just when there is pressure on the plunger held in place it seems to put off centre pressure on the piston that slows its return. Shall continue to play!

GeoffF7 (author)GeoffF72016-05-31

Sorted. When armed there is some downward pressure on the piston and I was getting some rubbing of the aluminium tube on the two tongues in the rear receiver when it returned. Sanded back and fast return now :) Thanks again for the great design.

samkoltisko (author)2016-03-01

Has anyone ever tried making a 3d printed paintball gun. Please reply back if you have already or plan to do so.

AKKID (author)samkoltisko2016-03-20

@samkoltisko Did you find what you were looking for becuase i've come across a couple

AKKID (author)samkoltisko2016-03-20

@samkoltisko Did you find what you were looking for becuase i've come across a couple

Street-Wise Irish (author)2016-02-18

Could I please see this in action ?! I am dying to see this !!!!!!!

Northbadge. (author)2015-11-20

Where does the bolt handle go? I can't seem to see it in the pictures, there's a slight error on my bolt handle, so I need to know if I need to reprint it (Didn't realize there was a hole, now there's abit of material in it)

Engineer777 (author)Northbadge.2015-11-21

If you drill the support material out of the hole it should be fine. You're right, I've just noticed it hasn't been covered well in the instructions. The bolt handles just bolt onto each side of the cylinder head (should be able to see them sticking out the sides in a photo of the final assembly).

SidharthM2 (author)2015-10-11

is a air soft barrel nessecarry? Where I live air soft is not huge, and you have to buy the guns from th U.S and shipping usually costs more than the gun. Can I use a break line?

Engineer777 (author)SidharthM22015-10-11

I've heard break lines have the right internal diameter, but it won't fit in the front upper receiver because the outer diameter (of the brakeline) is too large. You may need to modify the CAD file.
Alternatively, you can buy barrels from ebay and amazon at a pretty good price.
Let me know how you get on!

TomE9 (author)2015-08-14

How is the AEG coming along?

Engineer777 (author)TomE92015-08-15

Pretty slow progress unfortunately, uni soaks up the time. Am just working on the microcontroller, involving things like shot control (burst, rof, precocking), a mini OLED display (for shot count/fire mode/reload warning), and potentially auto adjusting hop up.
This is a project I want to do a quality job of though, i.e. it will take a while. Looking at finishing in the next two years.

TomE9 (author)Engineer7772015-08-15

Sounds awesome man, Uni definitely kills your time, hence me looking for builds rather than developing my own haha.

Engineer777 (author)TomE92015-08-16

Good call haha. I have definitely tapped into the plethora of open source designs more than once!

jjack08 (author)2015-06-30

So cool to know about that, but I prefer buying all asg equipment in shop.

rhofstad made it! (author)2015-06-11

Well, there it is... Finished and displayed with its older brother :-)

I have to see if I take the time to paint it later on. I sort of like it as it is for now.

Thanks again for the design Sam and I look forward to the next! :-)

Keep up the good work man!!

rhofstad (author)2015-05-31

Hello again :-)

Wow. Another great design from you... I think... I... have to make this one too! :D

One question:

What is the OD of that bike pump?

Just want to see if i already have a suitable pump before i go ahead and purchase one. :-)

and.. i have to tell you something...

I actually made the front page of a Norwegian men`s magazine (Printed magazine Called "VI MENN") with the first 3D printed air soft rifle (you posted the instructable of) :D

If you want to take a look at the web version of the article:

Engineer777 (author)rhofstad2015-05-31

Hi Roy,

That's awesome! Great to see the gun is getting used well :)
The bike bump for the submachine gun is the same one used for the bigger rifle, so just measure the one you have built. I'm not sure what the OD is at the moment, but there is about a 0.5mm clearance around the outside of the cylinder (1mm for the diameter), so it doesn't have to be exact.

Let me know how you get on.


rhofstad (author)Engineer7772015-05-31

aha.. 28mm ish then.. Ill see what i can find.. or maybe I will modify it to use an airsoft piston/cylinder... who knows :-)

I just tried to open the SLDPRT files but.. sadly I can not open them. It looks like you have upgraded your SW? I still have the 2013 edition and get "Future version" error message :/

Will post pictures, modifications and upgrades as I go on :D

Engineer777 (author)rhofstad2015-06-11

That's a shame about the solidworks files, if you're keen to do some modifications I could convert them back to 2013 versions next week. Let me know

rhofstad (author)2015-06-01

Next time...

PLEASE do a pump action shotgun!??? :D

with ejecting shells!!?? :D :D

Engineer777 (author)rhofstad2015-06-11

Funnily enough I have made a few initial sketches of a shell ejecting rifle! But my next project is an AEG with some cool electronic features... will let you know more as I progress later this year.

RichardC20 (author)2015-06-09

Hey do you take on work? theres an airsoft gun id like made but dosnt exist its from a concept? If you could email me at of we could get it to work id happily pay a commission

rhofstad (author)2015-06-07

Well.. I have assembled it (ish) still missing the stock cause i have to get hold of the alu for it first. But shoots and even recharge from the magazine! :D Still need a bit of tuning to make it smooth, reliable and shoot a bit harder but.. IT WORKS!!

Thanks for the design Sam!

Engineer777 (author)rhofstad2015-06-08

Awesome! What colour are you thinking of painting it? I think a tan would look great :)

rhofstad (author)Engineer7772015-06-08

Thanks :-)

Yes.. tan is what I thought also.. tan with the black that you see in pic I think..

rhofstad (author)2015-06-03

All the parts printed! :D

Now.. where is that auto-assemble-button? :p ;-)

obbm (author)2015-05-02

Hi, nice Designs!
I think of making a magazine for my Airsoft UMP so i'll maybe take some ideas from your designs ;)
I don't know where to get a long+thin enough spring so i'll try to use a rubber band too. Do you think a rubber band (or two) would be strong enough to reliably work for a larger magazine (the original is about 20cm long)? Also do you think it would work without the wheel? I don't think the friction of a rubber band is too high but i don't really now. By the volume of the magazine (3x4x20 cm) i would have enough space to put two or even more rubber bands.

About This Instructable




Bio: I am a Mechanical Engineering student studying at the University of Auckland in NZ. I am severely addicted to 3D printing, infected with a passion ... More »
More by Engineer777:Printable Airsoft Submachine Gun3D Printable Airsoft Gun
Add instructable to: