Having weapons be convertible between multiple completely different cartridges, could pose some technical, and balancing challenges, so a 5.56 NATO, 7.62×39 mm, and .22 LR AR-15 style rifle should probably not be different versions of the same weapon, but different weapons, with a high degree of parts interchangeablity. However, converting a firearm to use the same cartridge but with different a bullet diameter would be much simpler, more practical, and might even be beneficial to the game.
Instead of the single durability value of 3.X, barrels should have three qualities:
- Rifling, which would be comparable to real world twist rates, and rifling depth, it would impact spread, (the cone of fire) parts wear, and stability (how stable the projectile flies.) With use, rifling would decrease, and eventually, if overused, a barrel with deep, aggressive rifling (100%) would eventually be worn smooth (20%)
- Bore, IRL: bore diameter, it would impact compatibility with the bullet. If the bore diameter is smaller than the bullet diameter, parts will heat up and wear out faster. If the bore diameter is larger than the bullet diameter, spread and stability will increase.
- Heat, would be caused by firing, and decrease over time, hot barrels might have greater spread, parts wear, and chance of malfunctioning.
The barrel itself could have other impacts on weapon handling, ballistics, and part durability, but those values wouldn’t degrade with use.
The bullet used, in addition to having an impact based on compatibility with the barrel, would significantly impact ballistics, including, muzzle velocity, (how fast the bullet is going when it exits the barrel) drag, (how quickly the bullet slows down) drop, (how much the bullet falls as it travels) spread, and stability.
Terminal ballistics, such as penetration, damage, ricocheting/shrapnel and setting off special munitions, should be determined by the bullet, its velocity, and (possibly) the angle it impacts from.
When crafting bullets, the tools used should determine bullet diameter. If playing on a nonSwiss map, molds for casting 5.6 mm bullets would probably be quite rare, so players wanting to use firearms chambered for that cartridge would likely have to settle for loading it with 5.56 diameter bullets.
Atleast two types of propellant should be available, smokeless and blackpowder. Blackpowder is made by mixing charcoal, sulfur, and potassium nitrate. Smokeless powder is made by soaking cotton in sulfuric acid and nitric acid. In game, sulfur and sulfuric acid, or potassium nitrate and nitric acid might be treated as the same, but I think they should be atleast be two materials different between the crafting recipes of Blackpowder and Smokeless powder, to make crafting the two more different. The vats used for crafting cloth into smokeless powder could also be used to tan hides, and dye clothing. Propellants should have volume and quality. When two containers of the same propellant are combined, the volume of propellant is added together, and the quality of the propellant is the average of the two.
Propellant quality degrades over time. Low quality propellant has lower muzzle velocity, less muzzle blast, less heat, less parts wear, and a higher chance of malfunctioning. Higher quality propellant has the opposite effects. The amount of propellant used in a cartridge should be non-adjustable, and a fixed amount should be used for each cartridge, ie blackpowder .45-70 is always loaded with 70 grains of blackpowder. Blackpowder and smokeless powder versions of the same cartridge should be treated as two different cartridges, but some weapons should accept either in their magazines.
The cartridge case used should determine what weapons the ammunition can be used with.
Pellets should have increased spread from rifling rather than decreased. Shotgun shells can’t be necked down to smaller sizes, and shotgun bores don’t increase, if a smaller projectile is loaded into a shotgun shell, it is saboted not necked down.
sorry if some of this stuff doesn’t make sense, this took longer than I expected, so I’m pretty tired