Introduction: Rocket or Grenade Launcher Pistol

Picture of Rocket or Grenade Launcher Pistol


UPDATE: This thing has a very short range. If you build this, you would be lucky to get 150 feet. I have since taken it apart and rebuilt it with a 24 inch barrel.

Cost to make - roughly $15 plus cost of Mad Bull XM PB4 unit.

My cost to make - $3. I had almost everything I needed already.

The Mad Bull XM PB4 is a Rerservoir and Valve system for pressurized volatile liquid. For airsoft, this liquid is called Green Gas. When the Valve of the PB4 is triggered (opened) all the liquid flows out of the reservoir into the Chamber behind the Nerf Football. The liquid - being very volatile - QUICKLY vaporizes into a gas state. The volume of the Gas is hundreds of times Larger than the volume of the liquid state. This Rapid Expansion from liquid to gas is what Pushes the Nerf Football out of the launcher. For further explanation, please talk to your local high school science teacher.

UPDATE: I took this launcher apart and built a longer launcher. The new launcher is 24 inches long. It is a compromise between the pistol and the LAW which extends to 30 inches long. It abandoned this design because the range sucked.

Step 1: Tools and Materials


Dremel / Rotary tool with the following attachments
- Cut off wheel
- sanding drum
- shaper / cutters
Drill with assorted drill bit
Screw tap
scroll saw
hack saw
screw driver
Clamp (optional)

ABS or PVC Pipe 2" schedule 40
Shielded pipe coupler (see my M72 Law instructable).
aluminum bar
steel rod

Mad Bull XM PB4 airsoft grenade (also sold by RAP4).

Step 2: Make a Pistol Grip.

Picture of Make a Pistol Grip.

Get your piece of wood, your saw and your dremel. Carve out a pistol grip.

If you do not know how to do this, find an instructable on how to carve wood and how to use a dremel.

Step 3: Cut a Channel on the Rear Portion of the Pistol Grip.

Picture of Cut a Channel on the Rear Portion of the Pistol Grip.

A push rod needs to link the trigger to the lever that pushes the valve on the PB4 grenade. A channel needs to be cut into the wood for this push rod. Use what ever Dremel bit you have to cut out this channel. I used my cut off wheel.

Step 4: Trigger Well

Picture of Trigger Well

Make a channel or well for the trigger to go into. Same method as the channel for the push rod.

Step 5: Connect the Push Rod Channel to the Trigger Well.

Picture of Connect the Push Rod Channel to the Trigger Well.

Use your drill to connect the push rod channel to the trigger well. Make the hole wide so the trigger can travel.

Step 6: Make a Trigger

Picture of Make a Trigger

Make a trigger out of you aluminum bar.

Picture 1 - Measure and draw out a rough trigger shape. The two dots are: Upper Dot = hole for the push rod; lower dot hole for trigger pivot point.

Picture 2 - Test for clearance.

Picture 3 - shape the trigger

Picture 4 - Test trigger travel, fit, and clearance

Not pictured - drill out the dots.

Step 7: Pistol Grip, Trigger, Push Rod Assembly

Picture of Pistol Grip, Trigger, Push Rod Assembly

You may need to make a shim so the trigger does not move side to side or wobble. I used a piece of brass (picture 1).

Picture 2 - Trigger is now in place. Notice the brass shim.

picture 3 and 4 - test the push rod travel

Step 8: Activation Lever for the PB4 Grenade

Picture of Activation Lever for the PB4 Grenade

I purchased a small hinge for the activation lever. The lever is just a flat aluminum bar with a screw sticking out of it to depress the grenade valve.

Step 9: Pistol Grip and Grenade/coupler Assembly

Picture of Pistol Grip and Grenade/coupler Assembly

Connect the coupler containing the Airsoft grenade to a section of PVC/ABS pipe. Attach the pistol grip assembly to the pipe using a cobination of epoxy, bondo, hose clamps, zip ties, etc. What ever makes the pistol grip secure to the pipe. If using screws, make sure the screws are flush with the inside surface of the tube so the nerf does not get snagged on it. When using glues and epoxies, make sure the pushrod does not get any glue on it. Connect the push rod to the valve activation lever. All done!!!!

Fill with green gas, load your nerf vortex and play SAFE! Enjoy.

Outdoor test showed about 120 feet effective range due to much shorter barrel. Max range is roughly 150 feet.

Those familiar with Airsoft know that "Green Gas" is really propane and is really flammable. With that said DO NOT attempt to use a projectile that is on fire.


Step 10: Diagram of What Is Happening Inside

Picture of Diagram of What Is Happening Inside

Illustration of what is happening inside.

My sorry excuse of a drawing of what is going on side the launcher.

Pictures are in sequence.

Color Code

Red = Grenade
Orange = Nerf
Green = Green Gas
Blue = Valve
Black "T" = firing pin.

Picture 1 = Launcher ready
Picture 2 = Pin presses Valve
Picture 3 = Valve Open and Gas Explodes Out.
Picture 4-5 = etc....


LightningEagle14 (author)2015-11-19

For me, 100 ft is pretty far. Good job.

Thank you.

MrTinkerer (author)2011-07-20

nope. Does not work that way. Needs a liquid to gas conversion to propel the nerf ball

jgderuvo (author)2010-10-19

That's sweet!

malumalu (author)2009-10-03

where can you buy the madbull xm pb4 round?

bdogjhonson1 (author)malumalu2009-10-11

airsoft websites like evike but they are 40-60 dollars each.

pieman12 (author)bdogjhonson12010-03-20

could u buy an empty used on on ebay? or a new one on amazon

MrTinkerer (author)pieman122010-03-25

an empty used what?

pieman12 (author)MrTinkerer2010-03-26


MrTinkerer (author)pieman122010-03-29

All grenades are sold empty.

pieman12 (author)MrTinkerer2010-03-30

thanks im kinda new to airsoft and i thot making this would be cool

heavymetalman1 (author)2010-03-24

can i buy one off of you? i will pay more than the original cost to make, plus shipping.

It's not so much the cost of the materials that will get you as it is the cost of my hourly rate. I think 4 hours labor time is a fair estimate...

sbann5 (author)2009-11-19

how far dose it go ???

MrTinkerer (author)sbann52009-11-19

Not very far. About 100 ft. It sucks.

I scrapped the design and built one with a 24 inch barrel. The new design is now a shoulder fired launcher with a max range probably a little over 100 YARDS.

mazingbrainiac (author)2009-11-08

 how did you connect the hinge to the activation lever? or what sort of screws? and, did you just put the other end of the hinge under the metal part of the coupler? thnx

The hinge is attached to the aluminum bar using the screws that came with the hinge. The other end of the hinge is just tucked under the metal binding strap of the coupler.

bdogjhonson1 (author)2009-10-11

is there any way to take the grenade out? i plan on using it for airsoft and i would need to reload it. also will this work with any m203 40mm round?

MrTinkerer (author)bdogjhonson12009-10-14

I play airsoft too. The reason why i built this is because I neededsomething to give me that added edge on the airsoft field. I haveairsoft in mind when I build all my launchers.

Look at the current launchers in the market that use the 40mm grenades(example, Deep Fire M72). They require you to unscrew the back and plopin another grenade with a fresh charge of green gas. Well, if youhave to have multiple grenades at $40 a pop, that gets expensive fast.

Well, you say, "y not just one grenade, and keep refillingit?"

Hmmm, that goes something like this : FIRE > unscrew back >extract 40mm grenade > fill > replace grenade > screwback on > FIRE. Sounds like a lot of steps, right?

My Launcher goes  FIRE > refill grenade> FIRE!

which looks faster?

The short answer - No, you do not want to remove the grenade.

mazingbrainiac (author)2009-08-28

would it b ok to have the wood screws come down from the pvc pipe into the handle? because i'm using sorta old wooden saw handle. its in great condition, but it isn't long int he front or the back for wood screws like yours. any ideas?

I used wood screws too on my first build. I put the pistol grip on and marked how far in the screws went into the tube. I then removed the screws and cut them down so they were flush inside the tube. It was still rough and probably snagged the fins of the nerf football. Than is why I abandoned the screws and just used epoxy and bondo to hold the pistol grip to the tube.

so u basically glued it on? with epoxy and, bondo? aight thanks

be sure to sand the tube so the epoxy and the bondo has something to stick to. Use 60 grit sand paper.

mazingbrainiac (author)2009-09-20

is there a spring somewhere to keep the trigger from staying depressed?

The hinge at the back has a spring that pulls the trigger to the read-to-fire position.

aseaheru (author)2009-09-14

do you go softing with this?

MrTinkerer (author)aseaheru2009-09-15

I did once. I was very disappointed by the range. So I took it apart and built one with a 24" barrel.

aseaheru (author)MrTinkerer2009-09-15


aseaheru (author)aseaheru2009-09-14

multi tube ones = artillery

macingtosh (author)2009-08-21

i rather buy an rap4 one theyre a little bit cheaper but at least its profesoinal

MrTinkerer (author)macingtosh2009-08-24

I saw this one in:

It looks very effective. Looks like it runs of an air tank so no refilling per shot, very cool.

Colonel88 (author)2009-08-20

Is this reusable?

MrTinkerer (author)Colonel882009-08-21


macingtosh (author)2009-08-20

can you sell me one not that good with building this type of thing

pyro lucas (author)2009-08-16

do i absolutely have to buy a grenadey thingy? they are very evpensive!

MrTinkerer (author)pyro lucas2009-08-18

this instructable is what it is. If the system used something other than the airsoft grenade, then you would NOT need the coupler and the lever to push the valve. without those three things, this thing will be a completely different beast. At which point it goes off-topic of what this instructable is about.

killerkorn (author)2009-06-22

did you trim the ends on the ball. and heres a pic of mine, on the front of the barrel i added this cardboard tube and taped it up cause i was bored.

MrTinkerer (author)killerkorn2009-07-01

Yeah, trim 1/4 of an inch from the fins.

killerkorn (author)2009-06-23

yea sorry i got one more question, when your playing airsoft and using you bunker buster, does the paint you put on the handle come off on your hand?

MrTinkerer (author)killerkorn2009-07-01

nope. Used rustoleum. Paint stays on the gun.

killerkorn (author)2009-06-23

heres a better pic. of it

MrTinkerer (author)killerkorn2009-07-01

I love it. Looks great. The front grip is a great addition.

fenixxx13 (author)2009-04-19

I just built this launcher using a 24 pvc pipe 2 diameter
the first few shots were about 100-140ft perfect but, now its just reaching 50 ft not sure if its the green gas that I use but, im getting alot of silicon in the tube. I dont know if that is what is makign the nerf vortex or distance sliggish. Any suggestions?

Also did you have a problem with multiple firings. It seems that the grenade gets cold and has poor power coming out of the tube. Did you run into that problem?

MrTinkerer (author)fenixxx132009-04-23

There is a definite coold down effect that dereases range. I tend to let the grenade warm up before taking the next shot. the one you made looks just like the one I have on youtube. Thanks for sharing.

itak365 (author)2009-01-12

So... I noticed that you have one that seems like the M72 but nonextendable, but rughly the same size, and with sight and istol grip... would that be derived from using elements from both tutorials, or is it another thing entirely (aka, i couldn't just add a pistol grip etc.)

MrTinkerer (author)itak3652009-01-12

It is derived from this one. I used a 20" section of ABS tube. i also extended the wood block behind the grip to reach all the way to the coupler in the back. I did NOT use wood screws. Instead I epoxied the grip to the tube then re-enforced the connection with Bondo. Finally, I abandoned the push rod and instead used a steel cable to connect the lever to the trigger. It is just the big brother of this design. Range is equal to the LAW.

killerkorn (author)2008-12-15

sorry , this is actually a really good instructable i just got frustrated because i thought i was 65 bucks on a airsoft grenade

MrTinkerer (author)killerkorn2008-12-16

I stated in the INTRO from the very begining -

"Cost to make - roughly $15 PLUS cost of Mad Bull XM PB4 unit."

so I do not understand where the misunderstanding is.

For my personal use, i just purchased ONE XMPB4 grenade. I have built three(3) different types of launchers (see my youtube video) and I just move the grenade from from on launcher to the other. This means that I got a very good investment out of the $80 i spent to buy the Grenade.

MrTinkerer (author)MrTinkerer2008-12-16

Additionally, go to any online Airsoft store and look at the cost of a ready made M203, M72A2, AT4, or RPG. The Starting price for those is usually $125 up to $800. AND YOU STILL NEED TO BUY GRENADES FOR THEM.

All Serious M203 users on my field buy 2-5 40mm grenades at $40 each plus $125 for the M203. So say 5 40mm grenade plus one launcher and you are looking at $325.

And people complain that this project will cost $110?! if $110 is too much then go to an airsoft store and see how far that pocket change you got gets you.

timntek (author)2008-12-13

Yes read the stuff on the instructable. You cant make this from looking at a bunch of pictures.

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Bio: I like to tinker and create things. When I have time, i make stuff. The stuff could be as simple as my patent pending spoon-on-a-stick ... More »
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