Kartr, on 10 April 2012 - 10:08 PM, said:
This makes much more sense in realistic terms, the SLDF would have wanted to consolidate ammunition types to ease logistics. Picking say a 105mm round and simply firing more rounds per AC rating not only fits perfectly with what we see in the rules, but makes sense from a military perspective as well.
Unfortunately the canon fluff says that's not the case and so we have to live with 30mm-203mm caliber cannons.
AC/s fire multiple rounds so that 1 massive shell doesn't work, however this is fairly close to the most sensible way to describe AC/s. See above.
Actually the barrel length is extremely important. The longer the barrel the greater the accuracy, the longer the barrel the more time the gases from the propellent have to expand increasing the velocity of the round, etc. Furthermore having the shells "rocket themselves" once they leave the barrel will cause them to loose all the accuracy the barrel imparted. Your "rocket shells" would go careening off in random directions as the rocket motors kicked in. That's if you ignore the fact that they are "shells" and by definition shells do not have "rocket motors" nor are the described anywhere in the fluff as having rocket motors.
a few nitpicks now I am not military, but as I understand the physics (and we are at least assuming battletech gives a general nod to physics) kk (kenetic kill) and HE based rounds work dramatically differently A kk round wants to be as narrow (small of endpoint ) as possible because it works in general by striking a point on armor so hard that the armor effectively becomes liquid (fluid), and so flows around the penetrator thus being useless against it.
HE rounds on the otherhand "bigger is better" the reason this works is most modern rounds include "shaped charges" where the round generates a cone (or funnel) shaped blast additionally many rounds of this nature also (may) use special materials such as copper to form a "plasma or gas jet" penetrator. why this is important is that there is definately an optimum angle for maximum penetration and burnthrough effects assuming the optimum angle was ~45 degrees a 50mm diameter round is going to best penetrate armor ~50mm thick or less (putting its focal point exactly on the "rear" surface of the armor panel). on the other hand an identically operating 200 mm round would ideally penetrate up to 200 mm thick armor plate.
now on another note re rocket "shells" there is a thing called a RAP round, mostly used in artillery the acronym stands for Rocket Assisted Projectile these exist and have for years. basically it is a cannon or artillery round with a rocket motor attached (or built into its rear) it can be used to effectively give a cannon or artillery round a much longer "effective barrel length" by continueing to accelerate the round for several seconds after it leaves the barrel. plus considering many rounds are fin or spin stabalized you won't loose as much accuracy as you might think as long as the round doesn't tumble.
on a 3rd note battletech autocannon are burst fire cannons and always fire a number of HEAP rounds so an ac20 fires ~200kg worth of rounds every time you pull the trigger if it is firing 10kg rounds that means it will fire ~20 of them, if the individual rounds only weighed 5kg each it would fire 40 of them and if they weighed 50gk each its burst would be 4 rounds.
if for instance a faction had settled on a common autocannon shell size (say 100mm) just for convenience and assuming said 100mm shells did ~1 damage per, an ac2 would be firing ~2-3 per its short bursts and likely the cannon would have a significantly long barrel (for the size of the round) this would in 2 ways explain the long range accuracy of the weapon 1 long barrel and low fire rate
an ac5 using the same 100mm rounds would be firing likely ~4-6 rounds (nominal 5) and assuming the same rate of fire would have a medium-long barrel ie less inherant accuracy from the shorter barrel length, and a larger shell spread due also to increased burst duration
the ac10 would likely have a medium to medium-short barrel plus firing bursts of ~10-12ish rounds/shells
the ac20 would have proportionallt a short barrel, and fire bursts of around 20-24 rounds every "shot"
in the canon references there are notes of ac 20 cannons (I want to say the pontiac 100 off the victor) firing either a 100mm round, or firing ~100 rounds per burst
I know the marauder was specified as mounting a gm whirlwindwhich is noted as being a 120mm ac5 and fires ~3-5 rounds per burst
wheras the riflemans ac5's are closer to 80mm (or smaller) and fire significantly more rounds faster