Toob HPA Nerf Blaster

Introduction

This is the "Toob" blaster I designed, it is inspired by the Sten gun from WW2.

Like its predecessor I wanted it to be cheap and simple to make.

The whole blaster is designed around 40mm PVC waste pipe. It uses the Cosmic Nomad dump tank made by Roboman Automation.

Air Blasters – Roboman Automation
 

The rest is fairly standard HPA hardware, an MJVO 3 valve 6 or 4mm tubing and appropriate push fit connectors , m3 nuts bolts and heat set inserts.

Rough early FPS numbers with a 300mm Monkey Mods Barrel (450mm cut down).

160 FPS at 90psi
180 FPS at 100 psi
190-200 FPS at 110 psi

It would likely be easy to tune this up to low to mid 200s and all the way down to 100 FPS using different air restrictors and barrels.

The air tank and pusher/ram are stationary in this blaster and a new dart is loaded by sliding the mag well, breach and barrel assembly forwards and backwards again.

Firing Demo:
 

The design is subject to change and additions but works great as it is. There will likely be an imperial tube remix done for US friends. I have plans to change the mag detent to a ball bearing and maybe make a small picatinny rail for the top.

Updates

10-1-24 Redesign of the trigger body to make the quick disconnect come out the right hand side of the trigger body instead of the back of the main tube. This makes the air tubing much simpler and less likely to kink. This is a much better design. The back cap has also changed to make it solid now and a bolt run all the way through it into a head insert in the back of the trigger body. The stock has been thickened up again.

16-7-24 Added optional basic iron sights.

15-7-24 Added an alternative back cap designed for the Balystik male nipple. This is much more secure than the other one.

12-4-24 Updated files and added a mag well and detent cover that that uses the ball bearing detents instead of a printed on.

Ball Plunger, Stainless Steel Ball Plunger Set Threaded Spring Loaded Ball Detent Ball Spring Plunger 6 * 7mm Body Accessories Set Tool Kit 10-Piece : Amazon.co.uk: DIY & Tools

Printing

I have attached an image with the print orientations I used.

The core, breach, mag well and stock need supports. I used organic supports (automatic painting).

I have provided a pre split stock for smaller print beds (its what I used). I just split it in Prusaslicer but provided it as STLs in case you do not know how.

Assembly

Add head set inserts to all the 4.5mm holes in the breach, core holder, trigger body and end caps.

Take the thinner of the 2 bits of brass and push fit it into the core holder, run a bit of super glue or similar around the base to create a good seal. You might need to persuade it with a mallet.

Take the o-ring and place it in the recess in the core holder, I found it best to apply a small amount of silicon grease here as it seals better and stops the o ring folding. Then pop the core into the holder. You might find it easier to add the m5 push fit connector to the back of the core before you do this.

Cut to length a piece of the bigger brass to fit in the breach up to the thread and flush with the face of that part. It is only a small bit to create a seal with the “pusher”. Flare one end slightly, I did this using an old 12g c02 cartridge (empty), I placed it in the end and gave it a few taps with a mallet. Glue this into the breach.

Next you need to line the PVC pipe up with the back edge of the trigger body and mark the 3 screw holes and the access hole to the body. Drill these holes and cut out the access hole and a small slot all the way to the back using a Stanley knife. Slide the core holder into the pipe and bolt up into it from the trigger body using m3x8mm screws. I found using hex heads with a ball ended Allen key made this easier (it can be fiddly). You way want to put some tube into the core first but it is possible using needle nose pliers afterwards.

Next temporarily bolt the trigger in place and position the MJVO3 valve in the trigger body with the push fit connectors already in place. I stuck mine down with strong 3M mounting tape but you could use glue or hot glue. 

Now you can connect up the rest of the air system to a quick connect and put the read end cap in place. Then bolt that in. Getting the bottom bolt in is tricky. I may change this design but for now remove the trigger and you can access the nut through the trigger hold using a ball head Allen key.

Now the rear is done. Take the the mag well and slide it over the blaster until it cannot go any further, make sure it is perfectly at 90 degrees then mark where the 4 screw holes are. Now cut a slot wide enough for the m3 bolts plus a mm or so. The slot should go 50-60mm further down the tube than the farthest mark you made, best to keep it shorter than needed then cut more out later, it is easy to do. Now temporarily pop some screws in the magwell in the slot just to hold it in place and mark on the tube where the mag cut out needs to be. Cut this big slot out with a Stanley knife, make sure it is a touch bigger than the hole, you do no want the mag catching on the tube as you insert it.

Now screw your barrel into the breach (careful not to over tighten and push the brass out). Slide the breach into the tube and use the barrel to rotate it so the screw holes are visible in the slots and the mag hole is face the mag well hole. Now slide the mag well over the tube and bolt in place top and bottom. Now you can test to see if when fully back the ram seals in the breach and fully forward completely clears the mag well. If it doesn't adjust your cuts and or the length of your ram. Add some thread lock to the mag well bolts but do not over tighten them as this will make the priming action too hard.

Now you can add the front end cap (after drilling holes for it).

Put the trigger body lid on making sure the trigger bolt is long enough to go through the lid and trigger and bolt into the heat set insert.

Add the fake screws to the opposite side if you like symmetry as I do.

Bolt the grip/stock to the trigger body.

If you have any suggestions or requests please let me know and I will do my best to accommodate them.

Happy Toobing.

For assistance with build etc head over to Roboman's discord server.

I decided to make my design free and availability for commercial use. If you want to support me or sell my design as a product please buy me a coffee.

https://www.buymeacoffee.com/darthtater