Airsoft M72 LAW Rocket Launcher




Introduction: Airsoft M72 LAW Rocket Launcher

Using an airsoft 40mm grenade shell for the reservoir and valve system, build a nerf launching LAW for about 60 dollars plus the cost of one airsoft 40 mm grenade shell.

WATCH THE VIDEO!!! - It explains how the launcher works.

Edit: People keep asking about the Strap/Sling. it is a 1 inch wide cotton webbing strap purchased at a local fabric store. Buy about 1-2 yards. Also buy velcro and 1 inch plastic buckles.

Edit 2: People STILL keep asking about the "Locking Mechanism". Seriously, it is nothing but a piece of plastic. But since I get questions on youtube, here, forums, private messages and email, I decided to make a video. WATCH the video in STEP 7.

EDIT #3: If others have a method to use a DIFFERENT GRENADE, Please Post a comment. Then we can Collaborate on making an instructable for using a DIFFERENT GRENADE. I have brainstormed methods of using other grenades but they all BREAK my Rule OF K.I.S.S. With that said, I ONLY RECOMMEND THE MAD BULL XMPB4 or the S-THUNDER GRENADE. Don't Ask me about other grenades.

Step 1: How It Works

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, 40mm type
Orange = Nerf Mini Vortex
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....

Step 2: Materials


2" schedule 40 PVC or ABS pipe 2ft or longer.

Fernco Proflex 2" CI, PL or ST to 1-1/2" Copper or 1-1/4"PL shielded coupler.
Part number 3001-215. Part number 3001-215. Part number 3001-215. Part number 3001-215.
(If you still buy the wrong part, I swear I will hunt you down and slap you!)

Fiberglass cloth tape 10"-12" wide by 2 yards.

1/8"x 1/2"x 24" aluminum bar.
1/2"x 3/4" x 1/16" thick aluminum angle - "L".
1" x 1" square wood dowel.

sheet of felt with adhesive backing.
roll of wax paper
24" lengtht mylar film
assorted screws and bolts.
Spray paint

1 Mad Bull XM-PB4 40 mm grenade ($80)
1 S-Thunder Multi-purpose Grenade ($65)
1 S-Thunder Foam Ball Grenade ($60)


Dremel rotary tool
--Attachments: sanding drum, cutoff wheel.
Drill and assorted drill bits
screw tap
plenty of latex gloves
dust mask
plastic cups for the epoxy
paint brushes
sand paper

My lightsaber - Not as clumsy or random... an elegant weapon for a more civilized age.

Step 3: Preparing to Fiberglass an Outside Tube.

Buy a section of 2 inch schedule 40 ABS or PVC pipe. I use ABS since it is less expensive and is black.

Wrap the pipe in wax paper.
Then wrap it again with mylar film. 

Measure out the length you want for the fiberglass tube and mark with a sharpie.

Place the tube on a stand or run a rod down the middle and suspend somehow. You need to be able to rotate the tube when applying the resin and the fiberglass cloth.

Step 4: Preparing the Fiberglass

Most people work with fiberglass matt for small projects because it is very cheap. However, I find using fiberglass cloth is much easier as we are working with a small diameter curve and cloth is more flexible. Cloth also gives a smoother finish.

Buy Cloth tape 10-12 inches wide by 2 yards long. Cut up the cloth to wrap the tube with 2-3 layers.

I had a choice between polyester resin and epoxy resin. I went with general purpose epoxy as it has no odor and does not shrink as it cures.

Step 5: Make the Outer Tube

Mix the epoxy and make the outer fiberglass tube.

Refer to resin instructions on proper mixing, mix ratios, cure time, and handling.

This is not a fiberglassing instructable. Search Instructables, Youtube, and Google on how to work with Fiberglass if you do not know how.

Step 6: The Coupler

Once the fiberglass tube cures, pull out the ABS tube inside (wax paper makes this easy) and remove the mylar film and wax paper. throw away the mylar and the wax paper.

Purchase a Proflex shielded coupler. Part number 3001-215. It is found in the PLUMBING section of ANY home improvement store.

Insert the ABS pipe in the coupler and tighten snug. The coupler is the rear section of the launcher. Insert the pipe / coupler assemly into the fiberglass tube and mark where it sticks out the front end.

Remove the ABS pipe and cut the ABS pipe so none sticks out past the fiberglass tube.

Step 7: Assembling the Outer Tube and Inner Tube Together

REMOVE the ABS/PVC pipe from inside the fiberglass tube.

Decide how much travel you want the inside tube to have when you extended your LAW launcher. I decided for mine it would be a 5 inch travel.

I marked five inches on the side of the fiberglass tube. Make sure the two points are parallel to the lenght of the tube.

Make sure to remove the abs/pvc pipe.

Drill out the marks.

Draw a line between the hole you just drilled in the fiberglass and cut out a channel with a dremel tool. Watch out for fiberglass dust. it itches and you should not get it in your eyes or breath it. Wear long sleeves, goggles and a mask.

Picture #3: Insert the ABS/PVC pipe back in the fiberglass tube with the COUPLER ATTACHED. Drill a hole in the ABS pipe at the front portion of the channel you just dremeled out.

Picture #4: Put a screw in the hole. Now the pipe will only move forward and backward a predetermined amount (mine is 5 inch travel)and the inside tube will not rotate.

Step 8: Control Box and Locking Mechanism

Figure a way to make some sort of control box on top of the outer tube. I used sections of a 1 inch square pine dowel. I epoxied it to the top and reenforced with more fiberglass and felt.

Once the epoxy cures, paint your choice of colors.

EDIT: Picture 2 & 3 - The Locking mechanism (13 seconds into the video)

This is a strip of plastic glued to the side of the launcher.
Nothing special needs to be purchased. Look around your house/environment for a strip of plastic at least 1/8 of an inch thick and about 3 inches long. It needs to flex without breaking. Look around and use creativity and imagination.

Drill a hole on one end for the screw in STEP 6 to go in to. Glue the strip of plastic to the side of the tube in such a way that when the launcher is extended the screw goes into the hole in the plastic. put a layer of fiberglass, felt or duct tape to make sure the plastic does not come off or shift (see the green square in picture 2). a flexible strip of metal will work too.

Edit: People still don't get how to make locking mechanism. I still get messages about it. I think the trouble is people are trying to make it more complex than it really is. The rule is K.I.S.S. Here is a video of the locking mechanism.

Step 9: Install Airsoft 40mm Grenade Shell

I chose the Mad Bull XM PB4 40mm grenade shell for three big reasons.

1. It has the fill valve in the back.
2. It has a large gas reservoir.
3. It is loud.
4. Is has the fill valve in the BACK.
5. Mad Bull has the reputation of being dependable.

These are normally used in M203 grenade launchers.

Orient the fill valve towards the bottom for easy filling.

Step 10: Trigger Rod

I used a a 1/8 thick by 3/4 inch wide aluminum bar. Iron or steel bar will work too. So will a round rod of some sort. Do what ever is best for you.

Picture #1: Measure from the center of the XM PB4 grenade valve (the silver circle) to the top of the control box. Transfer that measurement to one end of the trigger rod. Bend the trigger rod 90 degrees or more. shape and bend the tip so that sliding the trigger rod forward will depress the grenade valve.

Picture #2: Cut the long end of the trigger rod/bar to match the lenght of the control box. Depending on the material used for the trigger bar/rod find a away to secure it to the control box. I used a flat bar so I used "L" brackets to hold the bar captive.

Picture #3: Attach something (screw, rod, d-ring, etc) to the bar so that you can grasp it and push the bar forward which will depress the back of the XM PB4 40 mm grenade shell.

Make sure that when you Extend the launcher the something above (screw, rod, d-ring, etc) has clearance to slide backwards unhindered. When the launcher is collapsed, you want something to hinder the something above from moving forward as a "safety".

Picture #4: *Optional*
Install a spring to prevent the trigger from accidentally pressing the valve.

Pictures #5-10 are to help visualize the whole mechanism.

Step 11: All Done

All finished. Congratulations!!

Fill with gas, insert rocket, and FIRE!

WATCH THE VIDEO!!! - This was in a parking lot.

I zoom in to where the rocket landed but I think it bounced off the trees at the end of the lot. We have hit the blue and white company sign past the trees, which is another 50-70 feet accross the street.

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.


Remember to to be safe and careful.

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    3 years ago

    I wonder if you could make this reloadable by sticking the spring closer to the trigger and putting a hinge on the bar in back


    8 years ago on Introduction

    hey i know a way to make one that fires any 40mm grenade. not quite as simple as yours, but very realistic. i had bought an m72 body, de militarized for training. i put a 2 inch barrel in it. i drop the grenade in the back, slide in a actuator from an automotive power door lock, and close the back. i was able to get the body for $50, the actuator for $8, and the small 7.2v lipo battery that powers it for $15. oh, and the fire button for $2.


    9 years ago on Step 11

    Is the Fiberglass just to make the outer tube, or does it also help reinforce the PVC, I want to make one of these, but if I don't require all of the fiberglass and additional parts and I can make a more basic version that would be great, but I was concerned with having pressure in the PVC tube.


    9 years ago on Introduction

    hey so far ive made one for my friend and am making one for myself i also have a 3D printer so i designed a trigger for it and also am going to design a part for that goes on the aluminum rod to depress the button is here is the link to the trigger


    9 years ago on Step 7

    Building one as we speak, this is like 3 years in the making. I'll post a video once I'm done. Basically building to the schematics of this instructables, with a few minor differences. I'm using very similar parts, with the exception of a few, namely the grenade, and the shielded coupler. I realize that what you have posted are the exact specifications for a product that will 100% work, though, being unable to acquire such items was difficult, as I am in Canada. I have a fair understanding of all the parts and realize that essentially you're just looking for a rear-load green gas grenade, and a shielded coupler which reduces from 2inches to 1.5 inches. If you are looking to make an airsoft grenade launcher:
    1. For a reasonable price
    2. That doesn't look like plumbing parts
    3. That is easily made within a week
    4. That will rival any $1000 launcher on the market
    5. Can be used on virtually any airsoft field
    6. Will not be turned down for use, as all potato guns are (even though they may be the most high-tech thing out there)
    And probably the most important part of this instructable, as all instructables by MrTinkerer:
    7. Sticks to the best principal - KISS: Keep It Simple Stupid.
    I have spent countless hours on the internet looking for a product that even rivals this, that is home made, for under $120.. Needless to say, there isn't anything close. Stick with this instructable, and be smart about it. If you read the directions one by one, carefully, as well as the comments, you will find literally EVERY answer you may have a question to. Even if you're a novice, this makes sense. Basically you could take the coupler, the grenade, and a piece of ABS or PVC and depress the trigger on the grenade with your finger, and you would have the most basic form of this weapon. The fiberglass as well as the externals are not required to make this weapon work. It just makes it much more functional.
    Thank you MrTinkerer, you are a god among men. No joke.
    I am going to school to be a gunsmith and machinist technician so I can start building my own guns, and eventually open the most bomb airsoft facility ever. I'm talking downed heli's, airplanes, indoor CQB, and outdoor scenario play. I have ideas to host a apocalypse day/week/month every year around halloween, where players will set out, and zombie-costumed staff by the 100's will attack unsuspecting players through ambush and surprise. Think COD and Battlefield maps, only real life. That being said, if and when I get my business up and running, I would love to work along side for your expertise and innovative standards in everything you do. Very impressed to say the least.


    Reply 9 years ago on Step 7

    Wow! so much flattery in the comment above. you are too kind. thanks. but, humbly, i am just a guy who likes to make stuff, nothing more....
    I am very much looking forward to seeing your launcher. Please send me a youtube link when you are done.


    10 years ago on Step 6

    Yes, whats important is that one end has an opening 1.5" or as close to 40mm as possible and the other end has an opening that is the corect size as the pipe you are using.


    10 years ago on Step 11

    Ive finished my law, and it turned out great. one problem i have is that the grenade (Mad Bull XM-PB4 Dummy Round BB Grenade Shell) will jam. after firing it once ore twice, the valve that is pleased does not come back out all the way. this makes it unable to be filled. i had my friend bring his mad-bull shell over and it did the same thing. did you have this problem? if so, how did you fix it?


    Reply 10 years ago on Step 11

    on airsoft grenades you need to push the button in until you hear a click with a pen or something similar and release this resets the grenade.


    Reply 10 years ago on Introduction

    Yeah. My mad bull does the same thing. I carry a nail for resetting the valve. Just press the valve all the way to the bottom. It will click when it is reset.


    10 years ago on Step 7

    Is there any substitute to fiber glass???


    Reply 10 years ago on Step 7

    If we wanted to go for carbon fiber, what would you recommend? Multiple layers like you did with the fiber glass? Single layer with a thicker sheet? I understand that using the fiber will probably make the build more expensive no matter what, but I'm just trying to minimize cost while making the outer tube (hopefully) more durable.


    Reply 10 years ago on Step 7

    Fiberglass will be significantly less expensive even if you did 5-6 layers. Fiberglass is very strong even with 2 layers.


    10 years ago on Introduction

    Just out of curiosity, would the launcher be able to fire loaded 40mm grenades instead of nerf balls? Like, if I loaded the grenade and left the nerf ball out, would it damage the weapon?


    Reply 10 years ago on Introduction

    This is still me. I've also noticed that it uses a different type of grenade. So, if I loaded a bb-type 40mm grenade, instead of the multipurpose grenade and Nerf rocket, would it damage the fiberglass tube?


    10 years ago on Introduction

    Hey where do you find nerf balls I already checked walmart they didn't have it and I don't know if toys r us has it. I know that Toys r us and everything discontinued their sale of nerf vortexes for some reason so where could you find those?