M72 LAW 37mm Sub-caliber Signal Launcher

BOM
(3) M4 nuts
(2) M4x8mm screws
(1) M4x12-15mm screw
(1) 1 5/8" OD fence post 23.5" long
Epoxy
E series rocket motor
3/16 OD brass tubing (steel brake line or copper line will work just fine too)
209 shotgun primers

Tools
Brake line flaring tool (harbor freight)
Allen wrenches
6.2mm drill bit (209 primer hole reamer)
Dremel with a metal cutting wheel
Positive mental attitude

To build the insert:
Print the front and rear bushings.
Epoxy in the fence post starting with the rear bushing. The two faces showin in blue should be exactly 14 inches apart.

Insert the 3x M4 nuts into the rear bushing.

The insert is installed with the LAW tube collapsed, and from the front. The longer M4 screw is indexed to line up with the slot under the primer. This prevents "real" ammunition from being inserted, indexes the insert, and assists in retention. The two recesses at the back of the rear bushing are clearance for the two rivets on either side of the primer slot on the launch tube. The shorter two screws are then tensioned against the inside of the aluminum rear tube.

Once the insert is installed, remove the two screws on the primer block at the top of the rear tube. You will need to keep the screws for the new back plate, but everything else isn't necessary.

To build the Bang Maker
Cut a length of brass tubing to 5.5-6" long (it'll get trimmed later) and flare one end with the flaring tool. The flare is what keeps the primer from blowing it out of the assembly.
Slide the brass tubing into the primer holder until the flare seats itself.
Set the primer plug onto the bending jig as shown, and bend the tubing around the jig by hand. There will be spme spring back, but that's ok, you can easily adjust it once out of the jig.
WIth the tubing bent tightly around the jig, mark the end using the 90 degree corner of the jig , and cut it flush. It's not a super critical dimension, but it's the nominal length.

Using a flat block of wood, with the tubing hanging between the jaws of a vise or something, press the 209 primer into the pocket of the plug.
Now you can install the booger hook as shown, and with the printed back plate, you're ready to install it. 

DO NOT ARM THE LAUNCH TUBE UNTIL YOU'RE READY TO FIRE AND YOUR BACK BLAST IS SAFELY CLEAR. 
The bang maker is installed ar the rear of the launcher, after the rocket has been inserted. Ensure that your brass tubing is pointed at the back/center of your rocket motor before arming.
Building the signal rocket
The rocket is an incredibly simple assembly. 
Slide your nose cone on with some line marking chalk in it, glue it in place if you like.
Using some clippings of filament as hinges, install your rocket fins as shown. The fin should swing freely. You may need to ream the hole in the fin, the base or both. A quich touch with a soldering iron or drop of super glue will fix the hinge in place.
Install your E size rocket motor.
As designed, the intent is for the rocket to go up in the air, and have the parachute charge disperse the line marking chalk for a fun display. After all, who doesn't want to do a gender reveal with a LAW?

You're ready to go! Aim your signal up in the air and send it in a safe direction!