S-Thunder M203 Grenade
I have dabbled in M203's and the various methods they propel stuff at you for well over 10 years. I started playing around with a Toytec M203 which was basically a machine gun in M203 form. I then moved onto the Tokyo Marui style launchers using the shell. These were a great way to have a version of their shotgun mounted to your gun. It gave you good range but only fired 3 bb's at a time. It was cool but was still lacking that little something a M203 needs. I then tried some of the propane powered M203 shells ranging from Madbulls to Vanaras. They were cool but still didn't have enough power. I had a Madbull M203 grenade that ran of CO2 and fired paintballs and other such things. It was cool but the seals ate themselves very early on.
While attending SHOT Show this year I ran into a company I had never heard of before. They had a selection of mines (reviews on these later), an M203 shell that could fire paintballs or anything smaller, and a shell ejecting AR paintball gun. While talking with the rep he told me that there M203 shell was capable of running on CO2. Not only was it capable of running on CO2 it was designed for prolonged use of CO2 at high pressures.
-Cheaper than other alternatives
-Capable of running on CO2 with a small and cheap replacement core
-Robust I have fired the system more than three dozen times on CO2 and a bunch more on propane with no ill effect.
-Great sound when fired
-Really easy to reset the primer
-In order to use reliably on CO2 you require a different core
-Not colored like typical 40mm military shells (however this is also a pro more on this later)
The S-Thunder M203 shell on the outside seems like a fairly standard shell for airsoft. However under its colored skin is a surprise waiting to be unleashed on its unsuspecting foe. Not only is this shell able to be used for airsoft but can be used by the scenario paintball player. This is done by having a hole capable of storing 4 standard sized paintballs in it. Now you may be asking how would the airsoft bbs stay in there won't they just flop out the end of the round? S-Thunder thought of this and have included a rubber end cap that fly's out like a slug with the pellets behind. You can purchase a bag of these slugs for $15.59 US and the bag includes 100 slugs. This saves you from looking around the field for a small red plug. If your cheap or don't like the idea of a rubber slug you can just wad kleenex in the end or put a piece of tape over the opening.
The standard core will last for a short while being used with CO2 but the seals will eventually go. Thankfully you can purchase a replacement CO2 core for $8.99 US. Personally I would have preferred this to be a feature in the grenade right from the start but at that price combined with the $39.99 US for the shell your still saving money compared to the $89.99 Madbull version. The replacement core is very simple to pop in. It comes with a nice thick grease to put into the 4 holes for the bearings. Once the bearing holes are greased up they just pop in and stay in place. Toss the spring in and put the primer on. Unscrew the shell of the M203 round and remove the assembly that was previously there and pop the new one in. This whole process lasted less than 5 minutes and can be done by just about anyone. This new core can be cycled for roughly 200+ uses on CO2.
Once you swap out the core you can fill the grenade with CO2 from one of the S-Thunder brand CO2 chargers or use the madbull one you might still have kicking around. Just slap it into your favourite 40mm launcher pull the trigger and fire away. Once the shell is fired to reset the shell to fire it once more just press the primer in and let it re seat to where it started.
I found this shell to be a very well thought out shell and continually had a smile on my face every time I fired it. However when on the receiving end of it I felt like I was getting hit by a good burst of rounds. This thing will be super effective in an urban setting. The three different body colors of the round allow for different loads. You can have .12gram pellets for spread or toss in some rubber balls for taking out a simulated tank. This product is great for the money and is almost half the price of its competitor.
A cross section showing the inner workings
The standard core
The CO2 Core