Introduction: Airsoft Rapid Fire Grenade Launcher Mod

The Built-in TAGinn Shell Grenade Launcher (B.T.S.G.L.) modification was designed to help Airsoft 40mm grenadiers become more effective by: 1) eliminating the needs to carry multiple shells, 2) removing the burden of humping multiple shells and freeing up the space to carry more projectiles, 3) minimizing maintenance time.

B.T.S.G.L. can launch 10 – 16 Tactical Game Innovation (TAGinn) projectiles with one 12 g CO2 cartridge, and more if hooked up with a larger air tank through remote lines. Since one TAGinn shell is fixed to a grenade launcher and modified to take continuous air source, there is no need to carry extra shells. The freed-up space on load bearing gear can be used to carry more projectiles or “shotgun clips” (BB shower). Furthermore, maintenance is simplified since there is only one TAGinn shell to care for.

This instruction is written with modifying a VFC EGLM grenade launcher in mind, but it is possible to modify similar launchers with sliding breech such as M203 and Strike Industry Havoc, or muzzle loading launchers such as RPG-7. However, I don’t have the time or money to verify whether or not the modification would work on these launchers.

Design History

When I completed the P.M.O.G. 2.0 project ( in 2014, I began toying with the idea of modifying my VFC EGLM grenade launcher so that it can launch projectiles without the needs of multiple shells. I came up with the idea after I saw the diagram and instructions from CrewChief’s Custom ( My original design was to tap an Eagle Force Multi-purpose Grenade Shell to an HPA air rig, but it seems rather cumbersome due to the long air line (Figure 1) .

In 2015, Tactical Game Innovation (TAGinn) announced their TAG 15 launcher project (, which featured a compact launcher using 12g CO2 cartridge as power source. The small size of the TAG 15 launcher made me change my design to use CO2 as power source as well. Incidentally, TAGinn launched a new shell model that uses unregulated CO2 as power source, so I planned to make use of the new shell model, as it would forego the needs of a regulator with the older shell model (Figure 2). Unfortunately, I didn’t expect that the push button valve on the air rig is only rated for 300 psi, and the fill port on the new shell model is recessed. As a result, I had to make use of the old shell model and add a regulator to the air rig (Figure 3). Even so, the complete system is still rather compact and performs well.

Safety Considerations

The B.T.S.G.L. modification comes with two layers of over-pressure protection. The TAGinn Shell Regular is rated for a maximum pressure of 450 psi, and the 3-way push button valve is rated for a maximum pressure of 300 psi. If gas pressure exceeds these limits, the system will become very difficult to operate, as the trigger and valve will freeze. At 300 psi, the TAGinn projectiles travels at an average of 117 fps, have the energy density of 1.58 J/cm^2, and can cause 3 mm of indentation on ballistic clay. At 450 psi, the TAGinn projectiles travels at an average of 174 fps, have the energy density of 3.44 J/cm^2, and can cause 7 mm of indentation on ballistic clay. Both gas pressures are well within safety limit of 44 mm.

Step 1: Acquire the Parts and Tools

Parts available from Palmers Pursuit Shop (

(1) 12g CART regulator (PPSP026) - $125

(2) *PARKER 68PLP-4-10X32 Male Connector, NP Brass, 1/4 In - $11.48

(1) .825”-14 female to 1/8 NPT female adapter (PPSP983) - $15

(1) 1/8 NPT male-male nipple (FITT013) - $3

(1) 10-32 plug (PNEU019) - $1.5

(1) 3-way 1/8 NPT to 10-32 push button valve (PNEU0355B) - $26

(1) macro line

* Also available from Zoro Tools EBay store (
(2) PARKER 68PLP-4-10X32 Male Connector, NP Brass, 1/4 In - $35.90 + $5 shipping for pack of 10 (


Parts available from most hardware stores

(1) 9/22 mm worm-drive clamp

(1) 1/2“ socket head

(1) 3 mm-wide zip tie

(1) 2 mm-wide zip tie


Parts available from some Airsoft stores (Amped, AirsoftMegaStore, Extreme Airsoft, etc.)

(1) TAGinn Shell Regular - $68

(1) TAGinn “Pecker” Projectile 10-pack - $42


Tools (available from most hardware stores)

(1) Dremel 200 or better

(1) Dremel tungsten carbide cutter (9903)

(1) Dremel cutting wheel

(1) Dremel sanding drum

(1) Dremel felt polishing wheel

(1) Dremel drill bits

(1) 1/8” flat head screw driver

(1) adjustable wrench

(1) 2.5 mm Allen key

(1) Loctite 242 (blue)

(1) teflon tape

(1) air line cutter (optional)


Tools from Shooting Chrony

(1) Shooting Chrony F-1 (optional)

Step 2: Air Rig Assembly

Apply Loctite and Teflon tape on all air rig threads (Figure 5). Turn the pressure adjustment screw clockwise till it’s all the way in (600 psi), and then back off about 3 quarters of a turn (Figure 6). Assemble the 12g CART regulator, .825”-14 female to 1/8 NPT female adapter, 1/8 NPT male-male nipple, 10-32 plug, 3-way 1/8 NPT to 10-32 push button valve, and 10-32 to 1/4 slip fit tube (Figure 7). Take off the filling valve on the TAGinn Shell Regular, and replace it with another 10-32 to 1/4 slip fit tube (Figure 8). Take care when installing the 10-32 to 1/4 slip fit tube – you don’t want to strip the tiny threads. Cut a 4-inch-long macro line, and use it to connect the two 10-32 to 1/4 slip fit tubes (Figure 9). Put the worm-drive clamp between the push button valve body and its 1/8 NPT socket to keep the socket from rotating freely.

Step 3: Air Rig Function Test

Install a 12g CO2 cartridge to the 12g CART regulator. Tighten the CO2 cartridge holder until no air leak can be heard. Make sure the TAGinn Shell Regular’s valve is at resting position by pressing the trigger button a couple times. Next, press the button on the push button valve and charge the shell. It may take quite a bit of force to press the button due to subpar pressure setting on the regulator. The push button valve is rated for 300 psi, but it is ok to go a bit higher at the cost of greater difficulties in operating the button. Since the shell is rated for 450 psi, I’d recommend setting the pressure between 300 to 450 psi, which should produce projectile velocity between 117 to 174 fps (36 to 53 m/s). It is possible to add a pressure gauge to the air rig and make pressure adjustment a but easier, but it’d make the air rig bigger and heavier. My suggestion is to use projectile velocities, measured with Shooting Chrony F-1, to estimate pressure settings. Once you are satisfied with the pressure settings, put the air rig aside and begin modifying the grenade launcher.

Step 4: Grenade Launcher Modification - Disassembly and Fitting TAGinn Shell

Disassemble the VFC EGLM grenade launcher until the breech base is exposed (see video: "B.T.S.G.L. Disassembly"). Position the shell with the air fitting at the center of breech base, and rotate the shell around its longitudinal axis until the air fitting is at approximately 5 O’clock position when viewing from the front (Figure 10). Also, verify that the air fitting will not hit the locking pins when it goes through the breech base (Figure 11). Mark the position of the air fitting at the front of the breech base. Use the smallest drill bit to make a hole at the center of the marked position, and increase the size of the hole with bigger and bigger drill bits until you can fit the tungsten carbide cutter through. Use the cutter to continue increasing the size of the hole until the air fitting can fit through. You’d want to create a hole that is barely bigger than the air fitting, so that you can secure the air fitting on the breech base afterward. Also, you will probably have to shave off some materials from the firing pin housing as well, so that air fitting can go straight through the hole. Check the position of the shell and make sure it does not impede the movement of the rotating breech / barrel. Afterward, use a 2 mm-wide zip tie around the neck of the air fitting to secure it and the shell to the breech base (Figure 11).

Step 5: Grenade Launcher Modification - Fitting Push-button Valve and Regulator

Use the 1/2” socket head as a guide to locate the position on the launcher cover for connecting the shell to the push button valve and regulator (Figure 12). Mark the position, and use the same method as before to create a hole on the cover that barely fits the socket head. Cut off part of the bottom of the socket so that the macro line can run smoothly through (Figure 13). Install the socket head on the launcher cover. Next, place the 10-32 to 1/4 air fitting into the socket head, and verify that the regulator will not impede the quick detach lever functions on the launcher (Figure 14). Determine the position for the 3 mm wide zip tie that will be used to secure the push button valve and regulator to the launcher cover. Mark the position, and drill two holes on the launcher cover to run the zip tie through (Figure 15). Place the breech base along with the secured shell on the launcher cover, and determine the length of the macro line to the push button valve and regulator. The macro line should run in a smooth arch from the air fitting on the shell to the one on the push button valve (Figure 16). There should be as few kinks on the macro line as possible. Shorten the macro line bit by bit until you reach its optimal length.

Step 6: Grenade Laucnher Modification - Removing TAGinn Rifled Barrel Threads

Detach the rifled barrel from the TAGinn shell body. Use Dremel sanding drum with low speed setting to remove the threads on the barrel carefully (Figure 17). When the threads are almost gone, check and see if you can place the barrel on top of the shell body without the needs to screw it in. If the barrel goes on, use the Dremel felt polishing wheel to smooth out any remaining irregularities on the inside of the barrel. Next, wrap some electrical tape around the outside of the barrel just enough to keep it in place inside the grenade launcher barrel.

Step 7: Grenade Launcher Modification - Switching Locking Pin Directions

The locking pin for trigger attachment is originally designed to move to the right side of the launcher, which would be impeded by the push button valve (Figure 18). In order to switch its direction while keeping the retainer clip, an extra slot need to be cut on the trigger attachment. First, remove the retainer clip and then the locking pin. Next, use Dremel cutting wheel set at low speed to cut a slot on the left side of the trigger attachment mirroring the original one. Insert the locking pin from the left side, and install the retainer clip on the newly cut slot (Figure 19). You are now ready to assemble the complete system.

Step 8: Complete System Assembly

Connect the macro line to the air fittings, place the breech base on the cover, and secure the push button valve and regulator to the launcher cover using the zip tie. Perform another air rig function test. If the test results are satisfactory, put all the small parts back on the launcher, and close the other cover as shown in the video.

Step 9: B.T.S.G.L. Shotgun Clip

TAGinn projectiles (pyro and non-pyro) are not suitable for CQB engagements, even though they are unlikely to cause serious injuries based on literature review and human subject tests. Real 40mm grenades cannot be used for CQB engagements, either. They have 14-meter arming distance, 130-meter casualty radius, and 5-meter kill radius. In other words, they can pose a danger to shooter himself as well as friendly forces. For CQB engagements, BB showers are safer and more realistic, just like the buckshot rounds on real M203 grenade launchers. With the B.T.S.G.L. modification, loading and firing a BB shower shell is no longer possible. But with the “shotgun clip” described below, B.T.S.G.L. operators can not only shoot TAGinn projectiles, but also BB showers.

You will need some paper towel, cheapest BBs you can find, and an 1.5-in ABS pipes in 1-in length. Cut the paper towel to the size of 6-in by 6-in, and push the center of the sheet to the bottom of the ABS pipe. Compact the sheet against the wall of the ABS pipe so that it forms the shape of a cup. Next, pour the BBs into the paper towel sheet to about 2/3 of the height of the ABS pipe, and close the ends of the paper towel to form a “tail”. Twist the tail to keep the paper towel from unwrapping, and apply a piece of paper tape to seal it. Lastly, apply a piece of paper tape across the top opening of the ABS pipe as well the “tail” of the paper towel. You now have a “shotgun clip”. To store “shotgun clips” in a pouch, keep the “tail” sides facing down, and stack them on top of each other.

To load the “shotgun clip”, you must align the “head” of the clip with the grenade launcher breech, push the “tail” of the clip until the paper tape tears, remove the ABS pipe, and continue pushing the BB-containing paper towel until it securely seated in the barrel.

Step 10: Operations and Functions

Step 11: Maintenance

Step 12: Marksmanship Training I - Fundamentals

Airsoft grenade launchers were used to be considered as shotguns or shoot-and-pray weapons. Now, with the availability of the TAGinn 40mm system (, TAGinn TAG 15 launcher (, as well as my Built-in TAGinn Shell Grenade Launcher mod (, the Airsoft 40mm grenade system has reached the level of precision and accuracy which we should give its marksmanship training some serious thoughts.

I am putting together a series of Airsoft grenade launcher marksmanship training videos adapted from U.S. Army Field Manual 3-22.31: "40-MM Grenade Launcher, M203". The first video, as shown below, will discuss the fundamentals: steady position, aiming, breathing, and trigger control. The second one will focus on the zeroing procedures. And the third one and beyond will investigate the combat techniques.

Although recoil is minuscule in Airsoft weapon, aiming is still paramount as the saying goes: “aim small, miss small”. If we review the purposes of the four marksmanship fundamentals – “steady positon”, “aiming”, “breathing”, and “trigger control” - we’ll see that they are as much about managing the recoil as keeping the sights on target. The purposes of “steady position” include keeping muscle fatigue from affecting the stability of aim and maintaining the alignment of natural point of aim with the target. “Aiming” is self-explanatory. The purpose of “Breathing” is to control the effect of breathing on the weapon’s movement while it is aimed at a target. Finally, one of the purposes of “trigger control” is to prevent sudden trigger pull from disturbing the alignment of the sights with the target.[U.S. Army, 2003] Another reason to conduct Airsoft grenade launcher marksmanship training is that the ammo cost is quite high. The large-caliber projectiles for Airsoft grenade launchers cost from US$ 3 to 10 each, which means players are shooting lunch money from each trigger pull. Although some projectiles are reusable, they are still likely to get lost during the chaos of gameplay. Therefore, Airsoft grenade launcher marksmanship training can not only help players perform better at games, but also keep their wallets full.


1. U.S. Army. Rifle Marksmanship M16A1, M16A2/3, M16A4, and M4 Carbine. (Field Manual 3-22.9). Washington, DC: Headquarters, Department of the Army; 2003

2. U.S. Army. 40-MM Grenade Launcher, M203. (Field Manual 3-22.31). Washington, DC: Headquarters, Department of the Army; 2003

Step 13: Marksmanship II - Zeroing Procedures

Zeroing procedures are defined as the steps to align sights to the projected grenade strike points. Although all weapons need zeroing, it is especially important for weapons with slow firing rates and limited ammunition capacity, such as a grenade launcher, in order to achieve high first-strike probability. Therefore, an overview of the zeroing procedures for Airsoft grenade launchers is warranted. I will be using my Built-in TAGinn Shell Grenade Launcher (B.T.S.G.L.) as an example for most of this essay.

There are three major types of grenade launcher sights: leaf sight, leaf sight with adjustable rear aperture, and quadrant sight. Due to the short weapon range in Airsoft, even with TAGinn system, Airsoft grenadiers need to put more emphasis on fast target acquisition than adjustability. I found out through experience that leaf sight is the best choice as one can transition between short and long ranges very quickly (i.e. 50 - 300 feet, very short compared to real steel. Real steel grenade launchers would still be on the first range marking when engaging the "long range" targets of Airsoft). Leaf sights are featured on M203, M320, and AG36. For the leaf sight with adjustable rear aperture on EGLM, you could use the distance markings as rear apertures without the need to fiddling with the adjustable rear aperture. But this trick won't work with M79's sight. Quadrant sights on M203, GP-25 and GP-30 provide more detailed and greater adjustment for ranges, but they are very slow for transitioning between short and long ranges. Due to these reasons, as well as greater availability of M203 leaf sight, I will discuss it solely in this essay.

M203 leaf sight may be mechanically simple compared to a quadrant sight, but it still features fully adjustable windage and elevation. There are notches on the sight that represent 50-meter increment in distances, and they range from 50 meters to 250 meters. In addition, the red mark represents 50 meters, and the “1” and “2” represent 100 and 200 meters respectively. My test showed that they can be roughly converted to 50 to 250 feet with the B.T.S.G.L.

Before describing the zeroing procedures, there are certain characteristics of the B.T.S.G.L. that must be discussed first. The chamber pressure produced by a fresh CO2 cartridge and the regulator is usually higher with the first charge – holding the push-button valve open for three seconds. The projectile velocity, as a result, is usually about 20-40 fps higher than the following shots. Also, holding the push-button valve open longer does not seem to yield any additional benefits, although it seems charging time shorter than three seconds sometimes fails to put enough gas in the chamber. A fresh CO2 cartridge has the most consistent pressure output from 2nd to 7th charges. So, if zeroing is not completed at the 7th shot, it would be best to swap out with another fresh CO2 cartridge. Next, it is possible to use any types of TAGinn projectiles for zeroing, but I feel it is best to use Paladin rounds as they leave distinctive marks on targets that make determining strike points easier.

The first step of zeroing is to find a suitable firing range. I recommend an open field about 50 feet long and 10 feet wide with a sturdy target stand at the end of the range. Although it may be more beneficial to zero at 100 feet as it is the most common Airsoft engagement distance, I feel the ease of zeroing at 50 feet justify some sacrifices in accuracy. A 3 feet by 3 feet or man-size paper target are best for zeroing, as well as practicing range estimation which will be discussed in Marksmanship III: “Range Estimation”. Next, mechanically zero the M203 leaf sight by putting the middle of windage and elevation scale on their respective index lines. Assume a stable position with your non-firing hand supported by a stationary object. Load a Paladin round, and align the front sight and the 50 feet / 50 meter/ red mark on the M203 leaf sight with the target. Fire the round, note the strike point, and adjust windage or elevation as needed. Repeat the loading, firing, and adjustment as needed. Zero is achieved when a strike point is near the center of the target.

I shot a Paladin and Venum round at 100 feet mark to validate zero. The Paladin hit slightly higher on the target, but I consider it a hit as it is within my standard of 3 feet by 3 feet window-size area. The Venum hit slightly lower, but considering it is a heavier round, it is not surprising. I was planning to test the accuracy of B.T.S.G.L. beyond 100 feet, but I ran out of ruler. Without knowledge of precise distance to the target, my shots went either over or short of the target, and were not captured well by the cameras. But I noticed they all flew very close to the target vector. In summary, with proper knowledge of the zeroing procedures, an Airsoft grenade launcher operating B.T.S.G.L. can achieve high first-strike probability if target range estimation is spot on. This brings up the importance of range estimation, which will be discussed in the next episode: “Range Estimation”.

Step 14: Marksmanship III - Range Estimation

Range estimation is defined as the determination of the approximate distances from the grenadier to the targets. It is paramount for Airsoft grenadiers as the trajectories of TAGinn projectiles resemble a sharp parabolic compared to that of BBs due to lack of Magnus effect and low velocities. Under recommended safety limit of 180 feet per second [REF 1], TAGinn projectiles will start to drop to the ground after travelling 50 feet, making it necessary to launch them at elevated angles in order to reach greater distances. The impact distances correspond to the launch angles, which can be adjusted through the use of grenade launcher sights. If the sights are zeroed correctly, and the distances to the targets are estimated accurately, a grenadier can achieve high first-strike probability by aligning the sights at the corresponding range markers.

There are four types of range estimation techniques: 1) "walking" the rounds, 2) appearance-of-objects, 3) visual aids, and 4) range card. "Walking" the rounds is not really a range estimation technique as the grenadier would not use the range markers on the sights at all. He would simply increase the launch angles gradually until scoring a hit. It may take a lot of rounds to score a hit, resulting in poor performance and waste of money. The technique is commonly used in video games as the grenade launcher sights are rarely modeled correctly in them. Appearance-of-objects technique refers to memorizing sizes and shapes of objects at different ranges and using the information to determine the distances to targets. It is most likely to be used in Airsoft games due to their faster paces and limited weapon ranges. They can be learned through simply "practicing" in games, but it is likely going to cost a lot of money from losing or using up projectiles. In addition, its accuracy can be affected by clarity of the targets, terrains, light and atmosphere. Although appearance-of-objects technique is used more often in games, it takes time to acquire. But it can be learned more efficiently through the use of visual aids, such as the grenade launcher sights or players' index fingers. By using the changes in height or width of the targets relative to the sights or index fingers, one can estimate the corresponding distances. In other words, grenadiers can memorize the relative height or width of common targets on Airsoft battlefields to the sights or their index fingers at 100 feet and 200 feet, and use the information to intrapolate or extrapolate the distances to them. Common targets on Airsoft battlefields include personnel, window, door, and vehicles. It should be kept in mind that the visual aid information will probably be specific to the users themselves due to differences in physiques and weapon setups between players. In order to maximize learning effects, it is recommended that grenadiers begin practicing on engaging targets at known distances of 100 feet and 200 feet, taking the time to employ both appearance-of-objects and visual aid techniques, and then move on to targets at various distances. Also, if the training exercises are done outside of games and dummy rounds are used, they can be recovered and reused, and will save players a lot of money.

The final technique, range card, is likely the most accurate method for range estimation. It requires time to survey key features around a position, and the distances from the position to them. The distances can be measured through map reading as well as pace counts. Once these information are recorded on a range card, grenadiers can estimate target ranges accurately by finding out their relative positions to the recorded key features. However, this technique is probably only applicable to defensive operations at larger MILSIM games which sometimes allow longer time to prepare defenses.

However, even with zeroed sights and good range estimation, it is still possible that the first round would miss. After all, the range is ESTIMATED. But what practicing range estimation techniques as well as other marksmanship skills will do is to minimize the amount of deviation, so that the second round's chance of hitting the target would be almost certain. Furthermore, under combat conditions, it is difficult for a grenadier to track a target, sense the impact, and reload the grenade launcher. Therefore, a grenadier performs best when working with a team as they can provide target tracking and feedback on the effect of fire, so that the grenadier can focus on operating the weapon. In addition, even with the extra space freed up on the load bearing gear from using TAG-15 or B.T.S.G.L. launchers, grenade projectiles are still precious commodities that can be carried in very limited quantities compared to BBs. Lion Claws only allows 4 projectiles on a single mission, and American Milsim only 12. Therefore, they are to be reserved for high-value targets, such as massed troops, strongpoints, or vehicles, instead of individual OPFORs. The target priorities should be decided by grenadier's assigned unit leader with the focus on helping to achieve the objectives. Based on these accounts, the next episode will discuss the techniques of working with a small unit.

REF: 1.

Step 15: Disclaimer

I do not provide goods or services, therefore I shall not be held responsible for any injuries incurred during the process of modification or misuse of the finished product. Please be aware that you'd void the warranty on your TAGinn shell and grenade launcher once you modify them. Always maintain your B.T.S.G.L. as you'd with your gas weapons. As this modification is probably going to be categorized as "homemade weapon", please check with your event organizers and field owners before using it in games. Never use it without event organizers' and field owners' approval!

Step 16: Questions, Suggestions, or Comments

Please feel free to contact me if you have questions, suggestions, or comments regarding the B.T.S.G.L. As I mentioned in the introduction, I do not have the time or money to work on other types of grenade launchers. If you have success in applying the concepts of B.T.S.G.L. on other types of grenade launchers, please do let me know! I'll make sure people know about your work on my P.M.O.G. Armory Facebook page.


Gordon Huang

Owner of P.M.O.G. Armory