The 40MM CANNON round
By GROG Copyright 2010 3LC Productions
I spoke with Scot Pace a while back concerning a new development in 40MM ammunition. The idea came while we were developing the M199 reloadable casing. The power of the casing was not enough to get good velocity on a substantial load of buckshot with a large 40mm opening. I thought why not reduce the ID of the casing to such that, the power loss would not be that great, and would maintain an ease of reloading. Scot and I worked together developing the new 40MM CANNON round. This is a self contained round of ammunition, reloadable, and powerful!
The round uses a modified XD casing base, with extended threads on the base sidewall, and a much larger powder chamber, capable of taking up to 18 grains of Bullseye. This is a massive amount of powder, considering the 781 practice uses only 7-8 grains to shoot a zinc projectile 400 meters. It is 5.115” tall, has a ID of a massive 1.060” (27mm!) Roughly a 4 gauge! The height of the chamber/barrel portion of the round is 3.690” above the vent screw plug. Scot has made some very nice wads in green plastic that closely resemble shotgun shell wads, to fit into these casings. They also include a cap to keep the shot in place, in the base of the wad. The wad has a pressure release area so it will slowly provide force to the shot load to throw it out of the casing. The casing is so powerful we needed to add a metal plate to the interior base of the wad so as to not stick the flechettes or shot into the plastic of the wad during launch!
The photo above shows one load of #4 buckshot with components
When I first received these new rounds, I could not wait to reload and range test them. I started with a 10grain Bullseye powder load, and a .010 copper wad. I used 80g of #4 buckshot in the wad, placed the cap on top, then loaded a ¼” thick foam wad in just a bit larger than 1.060”OD to help hold everything in. These worked very well, and showed no sign of pressure problems, so I increased slowly to 15 grains of Bullseye, where I got very good penetration at 10 yards on ½” treated plywood. 80g of #4 buck is quite a load of buck!
I next loaded and tested various flechette loads. The first loads were basically wads filled with rolled flechettes. These are those darts that are on rolls, with every other dart turned downwards such as this:
They pack really nice this way, and worked fine. Only problem I noticed was the tight grouping, most likely form the flechettes being all tied together in a large pack. I then decided to use the same method they are packed into the 155 howitzer shells, and use a center post. This would reduce the payload slightly, but still contain a lot of darts, and also it would make the payload a bit lighter for more velocity. I loaded them using a wooden dowel center post:
I wrapped the darts around the center post until I had enough to fit loosely into the wad interior. I then split them off the roll, and loaded them into the wad:
I then used loose darts to fill the rest of the interior, then pushed the wads down into the base of the casing. I used a ¼”thick foam wad to top them off, and hold the payload securely in the casing. I tested the different flechette loads and found that the dowel center post method worked best. I then loaded and prepared five more test rounds, loaded to 20g of Bullseye, made using the dowel method. I fired five rounds into the target, some of you have already seen the video of the range test for this round. Here is the link:
The overall performance of the 40MM CANNON round is fantastic. The lighter payload of flechette darts allows you to up the powder lift charge to 20 grains of Bullseye. This is a very powerful casing, so I do not recommend firing it out of launchers that are not Mil Spec, or of very stout construction with the 20 grain loading. Never use the 20 grain loading with lead shot! Lead is too heavy, and that loading will cause damage to your casing, or worse. When you reload these yourself, I recommend starting with 10 grains, and loading them until you discover a load where you are comfortable. Lead shot reloads, I recommend not exceeding 15 grains. Flechette loading can be done to 20 grains, but do so carefully, and at your own risk!
The finish of the 40MM CANNON is a very nice, gold and black anodized. I love the look! The sidewall of the barrel portion is milled to allow you to get a good grip on them when unscrewing the base for reloading. The primer pockets are stainless steel, and clean up very easily. The rounds I have tested and fired many times have YET to be cleaned, other than a quick brush of the primer pocket.
If you want a round for your 203 or 79 that you can depend on for everything from hut clearing, to terrorist perforating, this is your round. This is a no BS, hellishly powerful, munition for the 40mm series grenade launchers. Best part about them is, you can reload them forever. As long as you do not overload them, as I recommend above, these casings should last you a lifetime.
Here is a reloading guide I put together for the 40MM CANNON munition. Like I said above, do NOT exceed the recommended loadings.