Looking at the larger mutlicannon classes, we've got the following calibers and barrel lengths:
Class 3 Multicannon: 90 mm (approx. 3.5 inch) caliber, 4.7 m barrel length (including rotating barrel housing)
Class 4 Multicannon: 200 mm (approx. 8 inch) caliber, 5.5 m barrel length
Class 4 Cannon: 420 mm (approx. 16.5 inch) caliber, 9.4 m barrel length
Typical ammunition weights and muzzle velocities for the ammunition would be as follows:
90 mm: 10 kg projectile, 820 m/s muzzle velocity, barrel length 4.6 m, gun weight approximately 1 ton based on the 90 mm M3 tank gun on the M26 Pershing tank
200 mm: 120 kg projectile, 850 m/s muzzle velocity, barrel length 11 m, gun weight approximately 20 tons for autoloading version based on the 8 inch/55 caliber naval gun on various US Navy heavy cruiers
420 mm: 1224 kg projectile, 762 m/s muzzle velocity, barrel length 20 m, gun weight approximately 120 tons based on the 16 inch/50 caliber naval gun on the Iowa-class battleships
We're going to assume here that Elite materials use significant weight-reducing strategies for the largest guns due to significant advances in manufacturing or materials. That allows us to fit the gun weight for each weapon into their equivalent hardpoint mounts:
Class 3 Multicannon: 5-barrelled 90 mm gatling cannon, weight = 5 x 1 ton = 5 tons, does not require weight reduction to achieve 8 ton hardpoint weight
Class 4 Multicannon: 4-barrelled 200 mm quad reciprocating cannon, weight = 4 x 20 tons = 80 tons, requires 5X weight reduction to achieve 16 ton hardpoint weight
Class 4 Cannon: single-barrelled 420 mm cannon, weight = 120 tons, requires 7.5X weight reduction to achieve 16 ton hardpoint weight
Given that the weights of Elite ships are quite a bit lighter that we would expect for their size and volume, a 5-10X weight reduction for structural materials would seem achievable here so we're just going to assume that the guns themselves are light enough to fit into the hardpoint weight limits.
The question now becomes, how much would the ammunition weigh for these guns given the known muzzle velocities. The idea here is that the gun should still hit as hard as a modern gun of similar caliber, otherwise the barrel size is meaningless and it would simply be a large, weak gun that does little damage for its apparent calber. So for our purposes we need to get the muzzle energy for the projectiles to be roughly equivalent, which we can achieve using smaller projectile weights at higher muzzle velocities.
For the mutlicannons, we have muzzle velocities of 1600 m/s which is approximately twice as high as what the 90 mm tank gun or 200 mm naval guns are generating. That works out to 3.8X the muzzle energy for the class 3 multicannon and 3.54X the muzzle energy for the class 4 multicannon compared to single-barrel 90 mm and 200 mm guns respectively. This means we can reduce the projectile weights proportionally to achieve the same muzzle energy for the rounds. The Class 4 cannon, however, has a similar muzzle velocity to the 16 inch naval gun, which means it still needs to fire 1.2 ton projectiles.
Class 3 Multicannon: 90 mm: 10 kg projectile/3.8 = 2.6 kg projectile required at 1600 m/s to maintain equivalent muzzle energy, ammunition = 5.5 tons to store 2100 rounds
Class 4 Multicannon: 200 mm: 120 kg projectile/3.54, = 33.9 kg projectile required at 1600 m/s to maintain equivalent muzzle energy, ammunition = 71 tons to store 2100 rounds
Class 4 Cannon: 420 mm: 1.2 ton projectile, no muzzle velocity reduction at 750 m/s, 1.2 ton projectiles required for equivalent muzzle energy, ammunition = 120 tons to store 100 rounds
The limiting factor then for the weapons becomes the weight of the ammunition, which gives us the following specs:
Class 3 Multicannon: 90 mm projectile, 2.6 kg at 1600 m/s, gun weight 8 tons plus 5.5 tons ammunition = 13.5 tons total weight (1.7X the 8 ton hardpoint limit assuming no weight reduction of the gun, both gun an ammunition would fit into hardpoint assuming 5X weight reduction of the gun)
Class 4 Multicannon: 200 mm projectile, 33.9 kg at 1600 m/s, gun weight 16 tons plus 71 tons ammunition = 87 tons total weight (5.4X the 16 ton hardpoint limit assuming 5X weight reduction of the gun)
Class 4 Cannon: 420 mm projectile, 1.2 tons at 750 m/s, gun weight 16 tons plus 120 tons ammunition = 136 tons total weight (8.5X the 16 ton hardpoint limit assuming 7.5X weight reduction of the gun)
For the Class 3 multicanon the ammunition load is actually quite feasible to carry for a 90 mm weapon, although it does require storage of over 5 tons of ammunition in addition to the hardpoint itself. This doesn't require any special materials for weight reduction of the gun as it could easily fit within the hardpoint weight, and if we apply a 5X weight reduction for the gun then we can easily fit both the gun and ammunition within the 8 ton hardpoint weight. With the Class 4 multicannon however the required ammunition weight increases dramatically to 71 tons, which is still feasible for the larger ships to carry but the weight would definitely affect the performance of an FDL noticeably, and that's assuming 5X weight reduction on the gun itself to fit into the hardpoint. For the Class 4 canon we're dealing with 120 tons of ammunition as the weapon needs to fire 1.2 ton shells to actually have the power of a 16 inch naval gun. Note that this assumes zero propellant weight for the rounds and so it's the minimum projectile weight the weapons can fire if we want to ensure the weapons are at least as powerful as equivalent-caliber guns that can be produced using modern technology. Anything lower than these ammunition weights means the guns will be less powerful than their visual size would indicate and the assumption for these calculations is that we're actually firing a gun that is as powerful as its appears to be for it's caliber.
Essentially we're left with a similar issue to what we were dealing with earlier, except that instead of being limited by total hardpoint weight the limiting factor now is simply where to store all the ammunition if the guns are actually as powerful as their visual size suggests. For the class 3 multicannon this isn't really a problem to accommodate the extra weight, it still remains possible for the class 4 mutlicannon but would be a significant issue for the class 4 cannon. From a gameplay perspective the designers essentially haven't considered the ammunition weights at all and for most of the guns up to class 3 this could be accommodated with weight-reducing strategies on the guns themselves, but for the largest class 4 multicannon and class 4 cannon they would have to carry significant ammunition weight in addition to the weight of the guns.
Class 3 Multicannon: 90 mm (approx. 3.5 inch) caliber, 4.7 m barrel length (including rotating barrel housing)
Class 4 Multicannon: 200 mm (approx. 8 inch) caliber, 5.5 m barrel length
Class 4 Cannon: 420 mm (approx. 16.5 inch) caliber, 9.4 m barrel length
Typical ammunition weights and muzzle velocities for the ammunition would be as follows:
90 mm: 10 kg projectile, 820 m/s muzzle velocity, barrel length 4.6 m, gun weight approximately 1 ton based on the 90 mm M3 tank gun on the M26 Pershing tank
200 mm: 120 kg projectile, 850 m/s muzzle velocity, barrel length 11 m, gun weight approximately 20 tons for autoloading version based on the 8 inch/55 caliber naval gun on various US Navy heavy cruiers
420 mm: 1224 kg projectile, 762 m/s muzzle velocity, barrel length 20 m, gun weight approximately 120 tons based on the 16 inch/50 caliber naval gun on the Iowa-class battleships
We're going to assume here that Elite materials use significant weight-reducing strategies for the largest guns due to significant advances in manufacturing or materials. That allows us to fit the gun weight for each weapon into their equivalent hardpoint mounts:
Class 3 Multicannon: 5-barrelled 90 mm gatling cannon, weight = 5 x 1 ton = 5 tons, does not require weight reduction to achieve 8 ton hardpoint weight
Class 4 Multicannon: 4-barrelled 200 mm quad reciprocating cannon, weight = 4 x 20 tons = 80 tons, requires 5X weight reduction to achieve 16 ton hardpoint weight
Class 4 Cannon: single-barrelled 420 mm cannon, weight = 120 tons, requires 7.5X weight reduction to achieve 16 ton hardpoint weight
Given that the weights of Elite ships are quite a bit lighter that we would expect for their size and volume, a 5-10X weight reduction for structural materials would seem achievable here so we're just going to assume that the guns themselves are light enough to fit into the hardpoint weight limits.
The question now becomes, how much would the ammunition weigh for these guns given the known muzzle velocities. The idea here is that the gun should still hit as hard as a modern gun of similar caliber, otherwise the barrel size is meaningless and it would simply be a large, weak gun that does little damage for its apparent calber. So for our purposes we need to get the muzzle energy for the projectiles to be roughly equivalent, which we can achieve using smaller projectile weights at higher muzzle velocities.
For the mutlicannons, we have muzzle velocities of 1600 m/s which is approximately twice as high as what the 90 mm tank gun or 200 mm naval guns are generating. That works out to 3.8X the muzzle energy for the class 3 multicannon and 3.54X the muzzle energy for the class 4 multicannon compared to single-barrel 90 mm and 200 mm guns respectively. This means we can reduce the projectile weights proportionally to achieve the same muzzle energy for the rounds. The Class 4 cannon, however, has a similar muzzle velocity to the 16 inch naval gun, which means it still needs to fire 1.2 ton projectiles.
Class 3 Multicannon: 90 mm: 10 kg projectile/3.8 = 2.6 kg projectile required at 1600 m/s to maintain equivalent muzzle energy, ammunition = 5.5 tons to store 2100 rounds
Class 4 Multicannon: 200 mm: 120 kg projectile/3.54, = 33.9 kg projectile required at 1600 m/s to maintain equivalent muzzle energy, ammunition = 71 tons to store 2100 rounds
Class 4 Cannon: 420 mm: 1.2 ton projectile, no muzzle velocity reduction at 750 m/s, 1.2 ton projectiles required for equivalent muzzle energy, ammunition = 120 tons to store 100 rounds
The limiting factor then for the weapons becomes the weight of the ammunition, which gives us the following specs:
Class 3 Multicannon: 90 mm projectile, 2.6 kg at 1600 m/s, gun weight 8 tons plus 5.5 tons ammunition = 13.5 tons total weight (1.7X the 8 ton hardpoint limit assuming no weight reduction of the gun, both gun an ammunition would fit into hardpoint assuming 5X weight reduction of the gun)
Class 4 Multicannon: 200 mm projectile, 33.9 kg at 1600 m/s, gun weight 16 tons plus 71 tons ammunition = 87 tons total weight (5.4X the 16 ton hardpoint limit assuming 5X weight reduction of the gun)
Class 4 Cannon: 420 mm projectile, 1.2 tons at 750 m/s, gun weight 16 tons plus 120 tons ammunition = 136 tons total weight (8.5X the 16 ton hardpoint limit assuming 7.5X weight reduction of the gun)
For the Class 3 multicanon the ammunition load is actually quite feasible to carry for a 90 mm weapon, although it does require storage of over 5 tons of ammunition in addition to the hardpoint itself. This doesn't require any special materials for weight reduction of the gun as it could easily fit within the hardpoint weight, and if we apply a 5X weight reduction for the gun then we can easily fit both the gun and ammunition within the 8 ton hardpoint weight. With the Class 4 multicannon however the required ammunition weight increases dramatically to 71 tons, which is still feasible for the larger ships to carry but the weight would definitely affect the performance of an FDL noticeably, and that's assuming 5X weight reduction on the gun itself to fit into the hardpoint. For the Class 4 canon we're dealing with 120 tons of ammunition as the weapon needs to fire 1.2 ton shells to actually have the power of a 16 inch naval gun. Note that this assumes zero propellant weight for the rounds and so it's the minimum projectile weight the weapons can fire if we want to ensure the weapons are at least as powerful as equivalent-caliber guns that can be produced using modern technology. Anything lower than these ammunition weights means the guns will be less powerful than their visual size would indicate and the assumption for these calculations is that we're actually firing a gun that is as powerful as its appears to be for it's caliber.
Essentially we're left with a similar issue to what we were dealing with earlier, except that instead of being limited by total hardpoint weight the limiting factor now is simply where to store all the ammunition if the guns are actually as powerful as their visual size suggests. For the class 3 multicannon this isn't really a problem to accommodate the extra weight, it still remains possible for the class 4 mutlicannon but would be a significant issue for the class 4 cannon. From a gameplay perspective the designers essentially haven't considered the ammunition weights at all and for most of the guns up to class 3 this could be accommodated with weight-reducing strategies on the guns themselves, but for the largest class 4 multicannon and class 4 cannon they would have to carry significant ammunition weight in addition to the weight of the guns.
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