40mm Grenade Maintenance Part 2

In this second installment, Coop delves into his method of maintaining 40mm grenades and modifying them to be more reliable. Part 1 can be accessed here.

So, on to the actual maintenance of a shell.  99% of them unscrew.  Simply grab both ends and begin twisting in opposite directions.  It’s bound to come apart, along with a bunch of tiny parts that you’ll promptly lose.  Please do this over a workbench and not on your shag carpet… not that I haven’t done this over a shag carpet, but ease your way into mastering the 40mm shell first!

This particular shell immediately highlights a problem for me.  I did not remove the spring from the valve/button yet.  That button (right metal cylinder) is physically stuck inside the valve (left pointed cylinder with ball bearings in it).  Most malfunctions I’ve seen come from improper machining of the valve.  My maintenance corrects this issue.

After some prying and wiggling, the valve assembly comes apart.  It’s very simple.  The valve (left metal cylinder) has an o-ring that supports a gas seal when the shell is filled with propane.  There are 4 ball bearings that fit within the valve.  Some newer shells have captive bearings.  These are pretty sweet.  Older shells, like the Moscart, have 8 bearings, stacked in pairs inside the valve.  If you’ve never worked on one before, you will hate yourself.  [I’ll include] photos of the Moscart so you can re-assemble yours after all these years of sitting in a shoebox.

After the valve and bearings comes the spring.  The spring sits inside the “button” or “primer” or “activator”.  I’ve heard it call all these things.  I’m going to stick with button, since you have to push on it for it to work.  It does however sit where the “primer” would sit, on a real 40mm grenade.

With all these parts laid out in front of you, wipe them down with a paper towel.  You want to remove the factory crud/previous owner’s crap from them.

In short, the valve is pushed against the chamber which holds the gas.  When the button is pressed, the lips allow the bearings to slip out of place, permitting the gas pressure to overcome the valve, pushing it down against the spring, and releasing via the path of least resistance, typically out the barrel, pushing BB’s out with it.  This is how 90% of airsoft 40mm shells work.  There are some odd/weird ones out there, but that is beyond the scope of this document.  The big key to remember is resetting shells:

Older Moscarts:  You have to twist the two halves apart slighly.  You may even hear the spring seat the valve for you.  Otherwise you have to press on the button until the valve pops in place.  You’ll know it worked when gas stops escaping out of the BB holes when you attempt to fill the shells.

Madbull style modern shells and clones:  No twisting required, simply press on the button to push the valve back in place, sealing off the gas chamber.  You’ll know it worked when gas stops escaping out of the BB holes when you attempt to fill the shell.

Modern, space age shells:  Self resetting.  The spring is powerful enough that after enough gas has escaped when being fired, the valve is pressed back into place automagically and is ready for filling again.  Dboys VOG-25 shells do this.

Here is a closeup of the spring guide.  The spring sits inside the button (right) and the button fits inside the valve (left).  The bearings were left out of this picture.  It is difficult to see, but near the bearing holes, the rim of the valve is flat.  This is what is causing the button to hang up and the shell to malfunction.

Here is the valve in my hobby vice, ready to receive it’s repair.  You can better see the flat parts, as lighter colored metal, in line with the closest bearing hole, and the bearing hole toward the top edge of the vice (not the visible hole, but the one between those two… all bearing holes are 90 degrees apart, so the one opposite the bottom most bearing hole… a light colored flat edge)

Once secured in the vice, I beat on the insides with several hobby files (half round and round), until I am happy with the changes I’ve made.  I use WD-40 to control the aluminum dust and ultimately make cleanup easier.  Here it is in the vice, post filing, but unclean.  The button should slip in and out of the valve (with or without spring), even at funny angles, as sometimes your launcher will push on the button and cause it to shift to one side or pivot slightly.  This, and the shoddy cleanup after the machine shop is what causes problems.

Once filed and cleaned, and you tested the fitment of the button inside the valve (tab A into slot B).  Make sure it’s smooth and the button doesn’t hang up anywhere on the valve.  With good fitment, you are ready to lube and re-assemble your shell.  I use a repackaged variant of Dow 55 called “Sl33k”, which is a grease based lubricant used in paintball.  I bought a 2 oz tube 10 years ago, and it genuinely is a lifetime supply, though doing 55+ 40mm shells (WARPAC’s and my collection, I am putting a small dent in my stash).

You will apply a thin layer of grease to the o-ring on the valve.

You will apply a tiny “dab” of grease to one edge of each bearing hole.  This is a trick to keep the bearings from rolling out once lubricated.  The grease from the bearings will eventually hit the “lip” of the button, which is all the lubrication it needs.

Once lubricated, pop the valve back in to the “front” half of the grenade.

Pop the bearings back in.  Some of them legit need to be forced in, given crappy tooling and mass production.  You can hit the bearing holes with a round hobby file if you feel so obliged to.

Then, balance the spring and button inside the valve.  It’s okay if the button isn’t straight up.  The back half of the shell will sort everything out.

And where exactly is the back half in all these photos?  Another trick.  Since the front of the grenade is round, and you don’t have 3 hands, put the front half of the grenade into the back half as a stand, so you can work on the valve without having to perform a balancing act.

Then, when the valve is ready, lift the front half out of the back half, and screw the back half onto the grenade, like so:

Screw until finger tight.  No need to break out strap wrenches and measure torque or other such silliness.

Here is another one of Tascabe’s grenades.  Pretty much the same internal mechanism, despite it being a different shell.  I think this is either a 36 or 48 round shell, so it has less barrels, but it works the same way, and the base stand trick works on most shells too.

Pretty sure the factory that made this shell used either cosmoline or earwax.  It didn’t taste like either.  Clean that crap off.  There’s no need for it.  It isn’t doing anything helpful.  Don’t replace it with grease either.

This bearing isn’t magnetic.  The grease is causing it to stick to the back of my o-ring pick.  Completely unnecessary.  Clean that off too.  It will get some grease when you re-assemble the valve.

And there you have it!  A few tips and tricks to keep your 40mm’s running.  Now break out those M203’s, HK69A1’s, and GP-25/30’s.  Nothing says ambush like 120 bb’s spread among your buddies with a deafening blast!

To read part 3, click here.