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Components

     Items that might be found in Veracruz, at Styx, or from the Cartel, etc.

normal length 12 meters; cutting fees:  $0.50 for light pipe, $1.00 for medium and heavy, $1.50 for pumpkin;

while bursting ratings are not known, it's probably still in excess of 1500 psi

capacities are at 1000 psi or 100 psi; weights are for empty tanks; pressure ratings are for new, undamaged tanks

Examples

     A 3 meter long barrel, in a 100 psi system with a 5 liter tank and a roughly 40 mm bore can fire a 1 kg object 400 meters.

     A 2.5 meter long barrel, in a 100 psi system with a 22 liter tank and a roughly 75 mm bore can fire a 0.7 kg object 400 meters

     A 30 meter long barrel, in a 100 psi system with 2,000 liters of tank and a 254 mm bore can fire a 6 kg projectile 1000 meters.

PGun Mark 1

     This setup will be operating at a max pressure of 200 psi. It has two barrels, which can be mounted together or separately.

• shop compressor. 280 kg, $100.

• two 3-meter light well casings, for gun barrels. 84.6 kg, $5.20

• twelve "K cylinder" welding tanks. 732 kg, $48

• two sturdy butterfly valves. 2 kg, $10.

• pressure gauge to 250 psi. 0.5 kg, $2.

• twelve simple ball valves. 2 kg, $4.

• eight sections of steel angle iron, 7 m long. 77 kg, $7.

• about 30 meters of Schedule 80 wrought steel 2" pipe (920 psi working pressure, 7340 psi burst pressure); also unions, joints, thrust blocks, and other fittings. Pipe is 224 kg, $22; fittings 30 kg, $3.

     Total mass 1432 kg; total cost (not including salaries of workmen) $201.20. Salaries:  two experts at $10 per day each, two assistants at $2 per day each; 4 days work = $96. With salaries, shop rental, installation, etc., call it $300.

     The "below decks volume" is about 2 cubic meters.

PGun Ammo

Explosive

     104 mm, 4.23 kg mass (same as an 81mm mortar shell). Until you get some actual mortar shells, a roughly mortar-shell sized iron "bullet", with a wooden sabot (it's easier for the locals to make an accurately-dimensioned wooden object) to fit the bore and prevent scratches. An 81mm mortar shell contains just under a kilogram of modern explosive (typically Composition B for US mortars) -- 575 cc worth. FG black powder is 0.518 kg (just over a pound) -- black powder is physically less dense than Composition B. Maybe 0.2 kg for the wooden sabot; so the iron part weighs 3.5 kg.

Antipersonnel

     With the low velocity of the Pgun, engaging an individual person will be difficult. 3.5 kilograms of 00 buckshot is ~1000 pellets, plus the sabot at 0.2 kg = 3.7 kilograms. Damage from each pellet would be very low (they're fired at about 1/3 the muzzle velocity of a 12 gauge shotgun); let's say 1 point of damage each. The CoC damage goes from ... hmm, guaranteed lethal at the muzzle, let's say 30 points of damage, to 1 point at something like 80 meters. Armor performance might be odd, since while one pellet can't penetrate more than 1 point of armor, having 3.5 kg of buckshot bounce off of you at 115 meters per second would be bad!

PGun Performance

     One deduction from first pass at the math:  the 250 gallon propane tanks were way too big for a 3 meter long barrel ... most of the air was wasted at the muzzle. If you use two "K cylinder" welding tanks per shot instead:

     Surface area of projectile base:  0.0085 square meters. Barrel volume:  0.025 cubic meters. Chamber volume 0.1 cubic meter (two K tanks). Average barrel pressure during firing:  160 psi (1,103,161 pa). Average firing force:  9377 N. Acceleration, 2217 m/sec/sec (226 G).  Muzzle velocity, 115 meters per second. Fired at a 45 degree angle,  the maximum range would be about 1,000 meters.

     The shop compressor can fill a K cylinder to 200 psi in a few seconds:  probably faster than you can load the 'gun'.

     As an comparison for range calculations, the 81mm mortar:

     The "minimum range" is based on how much the shell might drift back towards your firing position while in flight nearly straight up. For your Pgun, I'd recommend 150 meters.  

     The usual rounds for a 40mm grenade launcher have a muzzle velocity of 76 meters per second. I'd say the Pgun would have an "over the sights" range of 100 meters, maybe 150 meters at most. Normal 20th Century buckshot from a 12 gauge shotgun has a muzzle velocity of about 340 meters per second.