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.
airsofter45 years ago
how did you get the end of the bar shaped like that inorder to press the m203 grenade?
MrTinkerer (author)  airsofter45 years ago
In one instance it was a combination of a bench vise and a hammer. in another instance it was a bench vise and a vise grip. Aluminum is not a hard metal, it is very easy to shape and machine.
scscdude125 years ago
 hey if u wana sell one of those practice laws tell me and put it on ebay
WarPigs DFW5 years ago
hello in pick 5..... the aluminum bar did you cut it, or can you keep it one long bar? Almost done with the LAW. just need to know. Thanks Alex
MrTinkerer (author)  WarPigs DFW5 years ago
Picture 5 shows my bar cut into 3 sections. I did that because it makes the bar more rigid. Keep in mind the launcher in picture five is launcher number 4. and each launcher before it was a learning experience. Fo your first build, keep it simple.
WarPigs DFW5 years ago
If I do need to cut it....how long are the cuts...
MrTinkerer (author)  WarPigs DFW5 years ago
you dont need to cut the bar... Yet. Once the build is complete. See how much excess you have when it is collapsed and how much the bar moves when you extend the tube. Cut the excess bar so nothing sticks out the front when you collapse the tube and still enough of the bar available for you to fully extend the Law. I can not give you exact measure because: 1. I do not know the dimensions of your LAW launcher. 2. I do not know how much your launcher extends. 3. The best person to judge would be the person next to it - you.