Improvised Grenade Launcher
The 40mm grenade launcher was designed as a close support weapon system for the infantry, and was intended to bridge the gap between the maximum throwing distance of a hand grenade, and the lowest range of supporting mortar fire. An area of between 50 and 300 meters. The M-79 and M-203 grenade launcher systems are presently in use by NATO forces and a great number of military and police organizations worldwide. These systems fire a single 40mm projectile at about 75 meters per second, out to a maximum range of 400 meters.
An M-79 40mm Grenade Launcher
The White Separatist will have use for powerful weapon systems like the 40mm M79 and M203 grenade launchers. The 40mm systems pumps projectiles out at low barrel pressures and spent casings for these weapons can be readily obtained at gun shows (at least in the US) or casings could, with the proper tools, be improvised. The US military designed the 40mm round to be easily reloaded by replacing the primer with a .38 blank. Civilian and law-enforcement application rounds, such as flare, tear gas and smoke are also available and can be modified to our use. These facts make the 40mm an ideal round to base an improvised grenade launcher upon. The design of these weapons is quite simple, not much more complicated than our improvised firearm designs.
This is a very simple design, but don't be fooled, it works very nicely. It is very similar in design to our "Slap" shotgun.
16" length of 1-1/2" (inside diameter) standard weight steel pipe.
9" length of 2" (inside diameter) heavy-walled steel pipe.
1-1/2" length of 1-1/2" steel pipe
2" long 3/4" bolt.
Three heavy-duty hose clamps (approximately 4").
Twelve 1/4" x 28 Allen screws 3/4" long.
One heavy flat washer 2" diameter, at least 1/4" thick and with no greater than a 3/4" hole.
Three 5/16" machine-thread nuts, 3" long.
One 5/16" machine-thread bolt 3" long.
One surplus rifle stock or improvised substitute.
Although the internal pressures from the 40mm are quite low at 2,600 psi (compared to 40,000 psi for most centerfire rifles) it is still wise to construct this weapon out of very strong materials. The barrel should be constructed from seamless DOM (drawn over mandrel) steel tubing. You may be able to scrounge this part from a scrap-yard but it is more likely that it will have to be purchased from a steel supply store. If you cannot find DOM tubing or if the price is outrageous, get the strongest tubing available.
For the breech, scrounge or purchase a 9" long piece of 2" diameter heavy-walled steel pipe. Standard-walled 2" pipe will not do for this application. When purchasing this part, be sure to specify heavy-walled 2" pipe. Have the shop cut the stock to specifications at use there reamer to clean up the cut. This will remove the sharp edge and burrs and leave a nice neat finish along the cut surface.
The barrel of a standard issue M79 is 14" but the operative may want a barrel that is slightly longer for increased range and accuracy.
Select a piece of standard-weight steel pipe with a 1-1/2" inside diameter. Check to see that it is the correct diameter by pushing an empty 40mm case into the pipe. The empty case should fit snuggly into the pipe if pushed firmly. You will later polish the bore so that the round drops in easily.
Test the two pipes by ensuring that the barrel piece (16" long x 1-1/2" diameter) will slide closely inside the breech piece (9" long x 2" diameter). It may be advisable to purchase both tubes at the same time to be sure that they are of the correct size. This may, however, cause the metal shop employee to ask some questions which the operative will not want to answer honestly.
You will also need a piece of 1-1/2" diameter pipe 1-1/2" long. This can be cut and reamed at the metal shop as well.
The hose clamps will be used to affix the breech piece to the stock. The operative may require larger or smaller hose clamps depending on the type of stock selected.
Polish out the chamber end of the barrel pipe until the 40mm case will slip into it without any trouble. Use very fine emery paper for this step.
Weld the 3/4" bolt on the other end of the barrel 3-1/2" up from the muzzle. Be sure to stand the bolt out perpendicular to the barrel, and weld it securely all the way around.
The 2" washer should be dressed down slightly using a bench grinder until it fits into the weapon's breech easily and evenly. Wear a pair of leather gloves while grinding the washer and let it spin freely against the grinding wheel. This will ensure even grinding and will allow the washer to fit smoothly into the breech.
Once the washer fitting is complete lay it on a large vise or anvil and place a 5/16" machine-thread nut in the center hole, being sure it is flat on the down side. Very carefully braze the nut into the center of the washer. Be especially careful to protect the nut's threads and to maintain its center alignment. This nut will eventually retain the firing pin, allowing adjustment of the pin in and out.
Lay the small 1-1/2" long ring of 1-1/2" pipe on the washer carefully and braze the two together evenly. The center hole of the washer must lay exactly in the center of the ring. Braze them all into one solid mass, again paying close attention to preserving the nut's threads in the center of the washer.
Using a 13/64 drill bit, make three opposing holes through the breech piece 3/4" from the rear of the piece. Tap them with a 1/4 x 28 tap. Try the new holes with the Allen screws, but do not set them permanently yet.
Slide the washer, with nut and 1-1/2" ring attached, into the breech pipe and tighten down the three Allen screws to mark the breech block ring inside. Withdraw the ring and drill shallow craters at the places marked. Replace the ring again, this time tightening the Allen screws and securing it solidly into the main breech piece. Torque down the Allen screws as securely as possible. Some of them might break during this process.
Making the adjustable firing pin is the only part of this project which requires any real machining. Using a hacksaw, cut the head off of the bolt and carefully grind the cut end flat.
Next, carefully wrap tape around the end of the bolt to protect the threads. Chuck the bolt, tape end first, into a 1/2" drill. This drill is about to become an improvised lathe with which the operative can turn the bolt into a firing pin. Clamp the drill into a vise or tie it securely to a tabletop.
Turn the drill on, rotating the bolt shaft. Using a 4" fine flat file, work the bolt down to a fine pin diameter of about 1/16" wide. Cut the pin back only 3/8" from the end of the bolt. When the pin is the correct diameter, put a sharply beveled point on it.
Take the pin out of the drill, remove the tape, and cut a shallow screwdriver slot on the opposite end with a hacksaw. The adjustable firing pin is now complete and ready to be screwed into the breech block piece. Set it in the block so that it barely protrudes through the washer and nut. If it is set too long it will bend or break, if it is too short it will fail to fire the round.
Secure the breech piece with firing pin installed, to the rifle stock using three hose clamps. Although the recoil from the weapon is more of a gentle nudge than a sharp kick, it is still strong enough to knock the breech piece loose from the hose clamps. Make sure that the three hose clamps are installed very tightly.
This is a very dangerous and powerful weapon and the same caution must be taken in test firing it as is used for testing the improvised firearms, presented earlier. Be sure to use military rounds during test firing (if possible).
How to operate:
Load the weapon and then, using the 3/4" bolt as a handle, slam the loaded barrel lock into the breech to discharge the weapon. This weapon produces very little noise upon firing and can be test fired in populated areas without much worry of alerting the authorities. The range of this weapon may be greater than the operative would expect, so use caution not to drop a practice round into your neighbors' pool.
If the firing pin has been adjusted properly and the breech is torqued in securely, there should be no problems. Just be sure you haven't cut any corners… this is a big, powerful weapon that can maim or kill you if things are not done right.
Burnish the final product with a wire brush wheel in your bench grinder, then apply a coat of flat black paint.
The portable mortar has, over the last 100 years, become an absolutely essential infantry weapon. It can be set up quickly, fired very rapidly and will drop rounds down at very high angles, making discovery of the mortar's position nearly impossible without modern electronic countermeasures. All of these factors make the mortar a desirable weapon for White resistance fighters. With a little practice the operator will be able to drop explosive rounds onto targets from a safe distance with great accuracy. The IRA has made use of a number of different improvised mortars, some of them very large, proving that it is not beyond the means of dedicated guerrillas to produce and deploy this type of weapon. The mortar system I will present is relatively cheap and easy to build, is highly portable and will perform nearly as well as a comparable military mortar. Ammunition for the improvised mortar is quite simple to produce with just simple home workshop tools, reusable practice rounds can be produced; allowing the resistance fighter to gain valuable practice with the mortar.
Most modern mortars use unrifled steel tubing for their barrels, meaning that their design is really quite simple. As with any weapon system, high-quality DOM tubing should be used to produce this weapon. Mortar tubes can be constructed from 3" tubing in just about any length from 18" up to several feet. Shorter length makes for a lighter, more portable mortar but the sacrifice is range. A length of between 36" - 44" will yield the most favorable results. A 40" long piece of 3" DOM tubing could cost as much as $120 new, which I think is a good price but others may not have the resources to spend in this way. Attempt to scrounge or "liberate" a piece of this material… try scrapyards and construction sites. If the operative is unable to locate DOM tubing, simple steel plumbing pipe will work since the pressures are not that high in this weapon.
If you choose to purchase the tubing, have the shop put threading on one end. Inquire about having a custom-made, solid steel end-cap made for the tube. This may cost a few bucks but it will be well worth it. Tell any curious shop employees that the parts are for a steel fence post pounder. If this solid steel end-cap cannot be obtained, a simple, off the shelf, cast end-cap will work but may develop cracks after several firings of the weapon. Whatever type of cap you obtain it will be necessary to drill a hole in the exact center of the cap. Use a center punch and start with a 5/32" pilot hole. Purchase a 3/8" machine bolt 4" long and two machine thread nuts of the appropriate size for the bolt.
Using a standard 3/8" x 24 die, cut threads from top to bottom on the bolt. Carefully sharpen the end of the bolt to a beveled point. Do not make a long, sharp point because it will break too easily. Drill out the pilot hole in the tube cap to 21/64". Thread with a 3/8" x 24 NF tap. Be very careful to thread the cap in a perfectly vertical manner. This is the most complex part the improvised mortar. An adjustable firing pin is required for the mortar to function reliably. The firing pin will be adjusted so that it just barely detonates the cap on the projectile when it is dropped down the barrel.
Place a locking nut on the back of the bolt. Thread the bolt through the cap with the pin extending through the concave portion of the cap. Extend the point up past the surface of the cap about 1/2". This is a trial-and-error procedure that is best done with inert rounds containing a primer but no propellant. Drop sufficient inert rounds till you are certain that the firing pin protrudes up through the cap just enough to detonate the primer and that it is centered properly.
Unscrew the cap off the tube. Using a camp stove, propane torch, or other heat source, melt about two pounds of plumber's lead containing at least 5% tin. After the lead is liquefied, pour it into the concave portion of the mortar tube end cap. Pour it only into the bottom edge of the threaded portion of the cap, not up in the area where it will prevent the cap from being securely screwed to the mortar tube. This quantity of lead will warp when cooling but, in spite of this, will cushion the cap, extending its life considerably.
Give the bolt firing pin a quick turn or two, loosening it as the lead hardens. After the assembly cools, tighten the buck nut down onto the back of the cap, securing it to the cap and lead buffer. It is imperative that the firing pin be adjustable in and out after the lead cools and that it be adjusted down so that the firing assembly reefs against the lead block.
Leading the cap will strengthen it, but after prolonged firing with heavier charges, the cap will still crack. It is best to make two or three extra caps at the same time rather than waiting until the first one fails during use and a replacement cap is unavailable.
Obtain a 15" long piece of 1" x 1/4" mild steel strapping. Use a piece of tubing with the same outside diameter as the mortar tube, hammer the strapping into rounds that clasp tightly around the tube.
Drill holes through the ends of the strapping and, using 1/2" bolts, securely fasten the strap about 12" down from the top of the upright mortar tube.
Purchase two pieces of 3/4" to 1" diameter steel rod 30" long, which will serve as bipod legs. Weld or braze two 1/2" washers to the top of each steel leg. Run the 1/2" bolt used to secure the tube clamp through the washers on the two legs. Since the legs have to move in and out a bit, it helps to place a couple of flat washers next to the welded washers. Ideally, the legs should flex in and out so that the tube can be angled up or down a bit.
These legs become an upright support for the mortar. The shooter can move them to provide more horizontal distance as opposed to additional vertical distance when launching the projectile. This arrangement is not very accurate, but it will function acceptably at ranges of 400-700 yards. Since the blast radius of the anti-personnel mortar bombs is about 30', the shooter doesn't have to have pinpoint accuracy to be effective.
Constructing mortar bombs is a bit more difficult, but shouldn't be beyond the abilities of anyone who puts they're mind to it. Purchase or "liberate" a 2" black, plumbing pipe nipple 6" long, two 2" end caps, and a 4" long 3/4" nipple. You will also need a 1/2" fender washer, which conveniently is just shy of 2" in diameter. Also obtain a 1/4" washer.
Find the exact center of one of the 2" end caps and drill a 5/32" pilot hole through one cap. If a 3/4" x 14" pipe tap is available, drill the center out to 15/16". Thread the hole in the cap so that the 4" x 3/4" pipe can be screwed securely into the 2" end cap. As an additional measure, braze the nipple top and bottom to the cap. This assembly must be exactly centered or it will misfire.
Measure down from the pipe cap 1-1/2" on the threaded 3/4" nipple. Working only above this line, drill at least ten 5/16" holes through the pipe, perforating it thoroughly. These holes bleed off the propellant charge from a 12 gauge shotshell when it fires.
A 12 gauge shotshell will fit nicely into the end of the 3/4" nipple. A small piece of electrical tape may be needed to bush the shell so that it does not fall out of the pipe during transport. Use only shotshell primers to test the mechanism. When certain that the mechanism is working, graduate to propellant and inert practice rounds.
Propellant should be 30 to 60 grains of Bullseye or Herco shotgun powder or a shotshell full of Hodgins' Pyrodex CTG. Exact loading will depend on the weight of the projectile, the distance the shooter wishes to fire and the quality of the tubing used for the mortar tube.
Dummy rounds can be made by filling the projectile body with 1-1/2 lbs of sand or some other convenient filler. Screw the cap on tightly and bush both end caps with electrical tape so that the round will fall straight down the barrel. A full 6" long piece of 2" pipe should be used as the projectile body so that sufficient distance between contact surfaces holds the propellant tube ( 3/4" tube ) rigidly in the center of the tube. Off-center propellant tubes are prone to misfires. Misfires will be a constant problem in the beginning. To correct these simply dump the round out of the tube, adjust the firing pin, change the end caps or straighten the 3/4" nipple on the round.
It will be necessary for the operative to test fire this weapon in order to work out the misfires and then to gain shooting experience. Paint your practice rounds red or silver to make them easier to retrieve and re-use. Don't even consider using this weapon in an actual attack until you have fired at least 100 practice rounds and can drop bombs on target after the second or third shot.
Building explosive rounds is relatively straightforward. Impact detonating rounds are much too dangerous for home manufacturers to attempt, therefore, I have provided instructions for building fused rounds charged with improvised C-4.
Start with a length of dynamite fuse which will provide 12 seconds of burn time before detonation.
Using epoxy, secure a small 1/4" washer inside a 1/2" fender washer. Fortunately, the outside diameter of the 1/4" washer just about matches the inside diameter of the 2" fender washer. Allow the two to dry thoroughly.
Push the length of dynamite fuse through the 1/4" hole and split it back about 1/2". Securely glue these split halves onto the washer face. Be careful that no glue gets onto the internal powder train of the fuse. Cut a match head from a strike-anywhere match and, using a little dab of contact cement or glue, fasten the match head into the center of the powder train. Crimp a #6 dynamite cap or an improvised blasting cap.
After securely fastening the bottom cap with the 3/4" pipe nipple attached, drop the fender washer and fuse in from the top of the projectile body. The fuse and match head should be pointing straight down the center of the propellant tube so that it can be reliably ignited by the blast of shotshell propellant.
Using epoxy, secure the fender washer in place within the projectile body. Be sure the epoxy is hardened before continuing.
Using a blunt wooden object, such as a tongue depressor, tamp a lightweight plastic bag into the pipe body. This is a difficult task, given the fuse and cap sticking back into the pipe center, but make sure every corner is filled with the plastic bag. This plastic liner seals the chamber and keeps air and moisture out of the powdered ammonium nitrate, which is easily ruined by air or moisture.
Carefully tamp in layer after layer of tightly packed, washed ammonium nitrate into the tube. Keep track of the amount so that the correct amount of Nitromethane can be set aside for later use. After filing with ammonium nitrate, seal the plastic bag and set the top end cap securely in place. Make sure that enough pressure is exerted on the fuse assembly, packing the powder into place. The force of the firing blank tends to dislocate the washer and fuse. Code the small plastic of Nitromethane and keep it with the round. Shortly before use remove the top cap, open the bag, and pour in the Nitromethane. Charged rounds can be held several weeks in this ready state, but storage of this type of ordinance is very dangerous.
12-gauge propellant cartridges can be prepared ahead of time. Remove the shot and shot-cup from the cartridge and then push a thumb-tip-sized piece of cotton as wadding over the powder and secure it in place with a bit of glue.
Building a functioning, reliable mortar, complete with high explosive rounds is not quite as easy as this brief description would indicate. Misfires, dud rounds and other problems will plague the operative at first… be patient though because this very valuable weapon can be completed with a little persistence.
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