my assumption was that the small bore ACs were like Magnum .22 rounds, super fast, low mass, not a large amount of damage compared to say a 30-06 - but still effective. they don't do as much damage, but the rounds get there faster, while the Large Bore (ac/20) were like shotgun slugs, they are travelling much slower but have much more mass, so they impart more damage. with the AC/5 and AC/10 being more like standard rifles.
we're talking also about the ability to penetrate massive specialized armor with massive slugs, so part of the range reductions were in my mind from air resistance. there is a good reason to not want to carry enough propellant to fire the AC/20 slug as far and fast as the AC/2. all that propellant will go boom if it gets hit.
just because the overall damage inflicted is bigger, doesn't mean that the round is traveling faster - in my opinion.
Unfortunately the two are directly related...
see a slow traveling but large in mass slug is not necessarily going to do more damage than a fast traveling but low mass slug (ie: not carrying more kinetic energy).
in fact the equation is in favor of the faster traveling one (basic physics) given the effect of the velocity is squared... compared to the mass where it's linear, this of course assuming that the projectile is going to do damage through kinetic energy with direct impact.
If the large autocannon, say AC-20 fired some form of slow projectile... then you don't need large propellant to do it... since the equation favor speed over mass and whatever kinetic energy the projectile is going to have you have to impart to it through the propellant (unless if it carry internal propellant ie: rocket). You need MORE energy (more propellant) to fire something faster, than you do to fire something heavier proportionally... so in order for the AC-20 to justify it's massive size and weight would logically entail that it has a massive energy transfer to the projectile (necessitating a large and heavy gun assembly to withstand the pressure), else otherwise if the projectile is a low velocity projectile... then all the extra weight and bulk on the gun is not necessary at all, the caliber may be larger, but a low velocity gun can be made much thinner and lighter compensating the caliber size.
Edited by Melcyna, 09 July 2012 - 09:45 AM.