Autocannon fire large caliber rounds that do most of their damage
through sheer force of impact. Standard Autocannon (or simply
ACs) are the most common type of autocannon. They are reliable
and do good damage with low heat build-up, but they weigh more
than other weapons and must carry several tons of ammunition
(15-20 shots minimum) to be effective. Larger autocannon make
good primary weapons for Combat and Assault 'Mechs. Most ACs
are too heavy to mount on Recon / Strike or Hunter Killer 'Mechs.
LB-X (Lighter Ballistics) autocannon can fire
two types of shells: a standard autocannon round and a cluster
round. The cluster round has a bonus to hit, and it fragments in
flight, peppering the target with submunitions. LB-Xs are able to punch through an
opponent's armor with standard rounds, and then fire cluster rounds
to increase the chance of getting a critical hit. Because a separate hit
location is rolled for each submunition, the chance of hitting a certain
location at least once with an LB-X 10 or -20 is pretty good.
LB-Xs weigh as much as other autocannon but receive less ammo
per ton. Be sure to carry at least two tons of ammunition for each
LB-X autocannon so you can use both standard and cluster rounds.
The Ultra AC 20 is the most devastating weapon a 'Mech can carry
and is the primary armament of many Assault 'Mechs. Ultra
autocannon weigh slightly more than standard
ACs, but they have greater range and they can fire two shells at
once, inflicting heavy damage with only moderate heat build-up.
Unfortunately, they are unreliable, hitting with both shots slightly less
than half of the time, and they go through ammunition quickly. Still,
they are good primary weapons if you can devote 3 or 4 tons to
ammo (20-30 shots minimum).
Caseless autocannon have the same weight and
range as standard ACs, but use lighter ammunition. Each time they
are fired there is a small chance that the shell propellant will
explode, destroying the autocannon. Of the new autocannon, the
Caseless is the closest to the standard AC and may replace it in
many designs. Although it lacks the special features of other ACs,
its extra ammo makes it a practical weapon and a good option if
you can live with the risk of propellant explosion.
The Hyper-Velocity (HV) autocannon is a neat
concept, but the rules fail to follow through with it; they neither have
significantly longer range, nor do they inflict more damage than other
autocannon. Also, they weigh more than standard ACs and, like
Caseless autocannon, there is a chance that their shell propellant will
explode, destroying the HV-AC. Unless your group adopts
alternate rules for the HV-AC, I wouldn't recommend using them. I
suggest allowing all HV-ACs to do 1.5 times normal damage and
giving the HV-AC 10 a maximum range of 24 hexes. These
alternate rules make the HV-AC a viable battlefield weapon and a
good primary system for Hunter Killers, Combat, and even Support
'Mechs.
The Gauss Rifle uses a magnetic field to
accelerate a water melon shaped metal projectile. It is the best
long-range, heavy-damage weapon available in the Inner Sphere,
and it has negligible heat build-up. Also, because it doesn't use
powder or propellant, its ammunition doesn't explode like missiles
or autocannon shells if the ammo bin is hit. The Gauss rifle itself will
explode, however, if it receives a critical hit. Because of its great
size, the Gauss rifle is most often carried by Support and Combat
'Mechs.
Machine guns have only meager range and damage potential. They
are useful for fighting infantry, however. The biggest problem with machine guns is that
they carry enough ammunition for 100 firings. You will never use
this much ammo so it presents a greater than normal risk of
explosion due to heat build-up or a critical hit. If you carry machine
guns, carry several so you can go through ammo faster and reduce
the risk of an explosion.