Post by mg on Jan 22, 2016 9:00:17 GMT
I drew a cartridge for Tenzin's autocannon. I was hasty, but it appears to be a 20x91mm. The total length of a whole cartridge would be 137mm, the same as a 12,7x99 (.50 BMG) cartridge. The projectile is 76mm long. The base diameter is 25,5mm, the shoulder diameter is also 25,5 (straight sides). A conservative estimate of powder capacity is 25 cubic centimeters, compared to 19cc's for the .50 BMG. I can't accurately calculate the recoil because I don't know the total weight of the weapon. However, a .50 BMG firing a lighter bullet at slower speeds from a 13,5 kilogram rifle produces 95 joules (70 foot pounds) of recoil force. I expect Tenzin's main weapon would break a human shoulder if it was fired without powered armor.
My goal for the new cartridge is to reach 1220 meters per second with a 61,5 gram projectile. It would have 45700 joules (33,700 foot-pounds) of kinetic energy at the muzzle. At one kilometer, the projectile has fallen 660 centimeters (260 inches, about 22 feet) assuming a G1 ballistic coefficient of .350 (a measure of how aerodynamic the bullet is, mediocre in this case). At one kilometer, it would still be moving at 396 meter per second (1300 feet per second) and would have 4880 joules (3600 foot-pounds). This does not count an explosive projectile, which are common for the 20mm caliber.
The smaller cartridge shown is a 6.5x51mm, which would be good for general issue. It has respectable power and trajectory, and it's made from a 7.62 NATO casing with a smaller-diameter bullet. Professional shooters with modern rifles commonly use this cartridge to win long-range target shooting competitions. Recoil is mild enough to fire rapidly, power is similar to a 6.5x55 Swedish Mauser: 9g (140gr) 855mps (2800fps) = 3300 j (2440 ft-lbs)
The bullet is fictional, based on the superb Nosler Partition bullet and modified to hunt humans instead of boar. There is an open air cavity in the tip, with a hardened steel cone to penetrate light armor. The copper jacket has a famous barrier that divides the core into front and rear halves. The front is likely to peel backward and fragment, but the rear core is lead with a full copper jacket. If it behaves as I hope it will, the heavy rear core will push the steel cone through armor plates. Damage within 700m is worst, but it remains deadly at 1,000m or longer if you can hit someone. If there is no armor, the weight distribution (heavy rear core, empty tip) makes the entire bullet tumble inside to cut a wide permanent wound.
My goal for the new cartridge is to reach 1220 meters per second with a 61,5 gram projectile. It would have 45700 joules (33,700 foot-pounds) of kinetic energy at the muzzle. At one kilometer, the projectile has fallen 660 centimeters (260 inches, about 22 feet) assuming a G1 ballistic coefficient of .350 (a measure of how aerodynamic the bullet is, mediocre in this case). At one kilometer, it would still be moving at 396 meter per second (1300 feet per second) and would have 4880 joules (3600 foot-pounds). This does not count an explosive projectile, which are common for the 20mm caliber.
The smaller cartridge shown is a 6.5x51mm, which would be good for general issue. It has respectable power and trajectory, and it's made from a 7.62 NATO casing with a smaller-diameter bullet. Professional shooters with modern rifles commonly use this cartridge to win long-range target shooting competitions. Recoil is mild enough to fire rapidly, power is similar to a 6.5x55 Swedish Mauser: 9g (140gr) 855mps (2800fps) = 3300 j (2440 ft-lbs)
The bullet is fictional, based on the superb Nosler Partition bullet and modified to hunt humans instead of boar. There is an open air cavity in the tip, with a hardened steel cone to penetrate light armor. The copper jacket has a famous barrier that divides the core into front and rear halves. The front is likely to peel backward and fragment, but the rear core is lead with a full copper jacket. If it behaves as I hope it will, the heavy rear core will push the steel cone through armor plates. Damage within 700m is worst, but it remains deadly at 1,000m or longer if you can hit someone. If there is no armor, the weight distribution (heavy rear core, empty tip) makes the entire bullet tumble inside to cut a wide permanent wound.
