Introduction: Airsoft M72 LAW Rocket Launcher
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.
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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.
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.
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
plenty of latex gloves
plastic cups for the epoxy
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
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.
6. IT HAS THE FILL VALVE IN THE BACK.
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
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.
I DO NOT CONDONE USING PROJECTILES THAT ARE ON FIRE, E.G. FIREWORKS WITH LIT FUSES IN THIS LAUNCHER. DOING SO COULD RESULT IN PROPERTY DAMAGE, ARREST, INJURY, AND/OR DEATH. USE ONLY SAFE, SOFT PROJECTILES ACCEPTED BY THE AIRSOFT/PAINTBALL COMMUNITY.
Remember to to be safe and careful.