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Deep Fire Grenade
A picture of a real Vietnam-era MK2 grenade. No BBs used in this one!
More flexible than most (in fact any) of the guys at the office!
A divider in the M26 grenade improved the blast effect drastically.
A dozen of repetitions with CO2 at 400 psi starts showing some marks.
The front corners are coming off here.
Flaring the middle section.
Fit the shell between material removals to get the best results.

You've seen it in the movies, you've done it in the games... Now it's time to carry it over to Airsoft! FIRE IN THE HOLE!

The Chinese have invented quite a lot of things, and not all of the inventions are aggressive in nature, such as fireworks. But some are, and a prime example of this are hand grenades, which, unlike fireworks, were certainly not used to drive evil spirits away.

Fast forward to the latter events of the second world war, we have "Die Amis" and "The Krauts" toe to toe in trenches and ruins on European soil. At close ranges like this, artillery and heavy grenade launchers can't be used effectively because of the high probability of causing casualties among your own side, so the individual soldiers carried grenades with them.



One of the most easily recognized model is the MK II fragmentation grenade, briefly mentioned in our GAMMA M-33 Claymore article. Its distinct pineapple shape has made it an icon in modern pop culture, and with the German Model 24 "Potato Masher" it is a widely recognized military item. The MK II sure looks intimidating with its deep grooves, which give the impression that it would explode into large chunks. However, the serrated surface pattern was only added to improve grip, and it doesn't affect the fragmentation. The MK II was used from WWII to the Vietnam War, and was then phased out gradually.

The M26 "lemon" is an updated version of the MK II. It has a smooth surface, which makes the grenade more suitable for rolling it over the floor, and improves the throwing characteristics as well. A lot of similar looking variants are adopted by various armed forces around the globe.

In 2006, Deep Fire released these two grenade models to the Airsoft crowd. Simulation grenades are nothing new under the sun, but they can be generally categorized in two:

  • Those that work really well
  • The others, which are available to civilians

    While it's generally more effective to simply spray a room with an AEG to clear it, playing Airsoft is also a lot about being cool (after all, a lot of people wear sidearms even to woodland games), and the MilSim groups should also not be forgotten here.

    As a result, manufacturers are developing products which would combine the aforementioned categories.



    The Deep Fire MK II and M26 grenades are supplied with an orange shell for better visibility, and to highlight that it's not a real grenade. A set of green shells is included in the box. The grenades are assembled, but you need to adjust the timer before using them.

    To adjust the timer, you need to separate the upper and lower body parts. Pushing the plunger shaft in the middle allows you to grab both ends to make the adjustments. It proved useful to make a mark on the part which remains on the inside of the grenade core, to use as a reference point when you adjust it. The exact adjustment is individual, but we found that opening the timer half a turn from the closed position is not enough. A 45 minute (3/4 turn) adjustment was found to be optimal in both of the test models.

    Should the grenade be a dud when you test various timer settings, wait for at least 30 seconds before picking it up, to reduce the risk of having it go off in your hands and face. As usual, safety goggles should be used at all times when handling the grenade. Turning the mock fuse, which sticks out of the top of the grenade, allows the gas to start hissing and will make the grenade go off. This should be done with great care! It's not a real grenade, but used incorrectly may cause bodily harm.



    Instead of only going bang, the Deep Fire airsoft grenades are also capable of blasting shells (three for the M26 and four in the MK II) in all directions. The shells fly up to ten meters (30 feet sic!) off the core when green gas is used in room temperature or warmer. This is no marketing speech. You can read the explanation and learn the trick later in this article, and see the video!

    The shells are constructed of a very flexible plastic, and they weren't damaged even when they were stepped on, bent on purpose, thrown around and blown off the grenade for quite a lot of times with high pressure propellants. You can most likely re-use them over and over just as long as you are able to find them afterwards! Painting the inside of the shells with a bright color is a good trick: It's not visible to the outside, but helps finding the shells.

    The external finish of the grenades is quite good, bearing in mind that the shells pretty much have to be plastic for obvious reasons. The handle and safety pin are made of steel, while the shells and collars are plastic with a nice rough texture. From a short distance it looks just like a real grenade!



    There is space between the core and the shells, which allows you to load BBs as well. However, as the amount and pressure of the propellant are limited, it is important not to choke it with too many BBs. This leads us to a question: "How to load less BBs without having them lie at the bottom of the grenade?" -Redwolf will figure it out!

    By taking standard 101 x 101 mm (a hair shy of 4 by 4 inches) paper notes and cutting them roughly in half, resulting in 101 x 51 mm rectangles, we created the prototype BB trampoline. (Yes, great innovations are sometimes simple!) The paper was just long enough to reach over the thick part of the core, and was secured in place by a rubber band. As the gas bursts out of the openings when the grenade goes off, the gas is trapped in a confined space created by the paper. Instead of going in between the BBs, the gas actually meets a more solid surface (not unlike a sail) and pushes it away with force. This improved the spread and distance of the BBs drastically.

    Another trick we tried was to prevent the BBs from going into the bottom of the grenade. After all, the gas is released from the highest quart of the grenade, so it makes sense to pack the BBs there. It took some foam from a box of Systema gears, scissors and less than a minute to make the filler piece to hold the BBs up in the top of the grenade. The combination of this and the paper trampoline seemed to yield the best results, but especially the paper trampoline was found to be effective. The MK II seems to be in a better position to begin with, because of its smaller girth and volume, so the effect of restricting the space is even more beneficial with the M26.



    The grenades seem to be a bit sensitive to temperature changes, but it is also important to make sure that it is fully loaded with the gas propellant. If the propellant is only loaded in gaseous form, it will not expand to a sufficient volume to produce a good effect. Some gas nozzles may fit too tightly to the fill nipple, preventing the remaining gas in the grenade from being replaced with liquid gas in the filling process. If this is the case, it may be advisable to make a small cut in the anti-leak O-ring, which is visible to the outside of the fill nipple, or remove the O-ring completely. We have had some reports of insufficient performance, and this is the most likely explanation: The grenade simply wasn't completely filled with gas! This trick is also most helpful, if your gas pistol is not getting as much shots as it should, and it has an anti-spill O-ring in the fill nipple.

    The new Mad Bull portable CO2 refill charger for 12 gram capsules arrived just in time for the mad (pun intended) pressure tests on the grenade. The refill charger proved to be handy and easy to use, and the only other thing you need is a standard 12 gram CO2 capsule. Starting from a healthy 200 psi pressure, we went up in 50 psi increments up to 450 psi. At that point the time from throwing to going off became so short that it's no longer practical. At 300 to 400 psi the bang was really loud, and the shells flew off with a happy pace. The lower body O-ring jumped out of its groove sometimes, but it's easy to reset. In regulated form, CO2 (just like any gas) can't be in a non-gaseous form, so while the pressure is high, it does not produce the same volume of gas flow compared to green gas, as long as the tank is filled properly. CO2 seemed to give a louder and more sharp bang, but in the end the shells and BBs didn't fly much further. It also stresses the grenade more, as you can see from the picture. We don't recommend constant use at over 300 psi for these grenades.

    It should be noted that gas pressure has a rather big influence on the timer. The higher the pressure is, the shorter the delay becomes. The grenade was originally designed for 134a or Top gas, so using a higher pressure makes the adjustment process rather fine. If you open the plunger shaft too much, the grenade will go off as soon as the handle (aka. "the spoon") flies off. Too much closed, and the grenade won't work at all.



    At first it sounds a bit funny. Why would you maintain a grenade? Well, in the case of Deep Fire, it's obvious. The grenade can be used over and over, so it only makes sense to ensure smooth operation from blast to blast by keeping it in a good condition.

    As usual with airsoft equipment with plastic parts, keeping the parts clean and a sufficient amount of silicone oil on them is all it takes to keep the grenade working for a long time. It really is this simple, and the harder part may actually be bothering to do it.

    Speaking of smooth operation, we found that the three shells of the M26 variant hug the core and collar so closely in the bottom, that they don't work optimally. Fixing it only takes a sharp knife, a steady hand and a couple of minutes. It is important to avoid shortening the shells, just flaring them is enough.



    All in all, the Deep Fire grenades seem to work really well for the intended purpose. The main benefit is the ability to use them safely and legally everywhere, because they don't contain any pyrotechnics. No special accessories or tools are needed for operating and loading them, just the gas and BBs are enough. Chances are, you are already carrying them for your GBB pistol!

    While the performance was a slight bit lacking in the beginning, the improvement was drastic when we learnt how to use the grenades properly. The Deep Fire MK II and M26 represent what we think is at the moment the leading edge of airsoft grenades. To put it short, a great bang for the buck!