Posted 12 March 2012 - 05:06 AM
I won't lie - guns on legs aren't the most efficient design concept.
However, they're not quite as uncommon as you think. First of all a "Leg Mounted" weapon often means that it's attached to the hip. An example of this is the Unseen Crusader (Or if the stats matched the artwork, the Summoner/Thor and the Hellbringer/Loki). Some - but very few - mechs also mount weapons as low as their knees (Viking, Sirocco), but they're pretty few and far in between. This might be for aesthetic reasons, or it might be because the stats don't have room for them anywhere else (A torso slot has only 12 locations, after all). Another reason might be for redundancy - If you blow off a torso location, all the components in that location get destroyed, and the arm gets blown off, losing you double the gear. The only way to blow a leg off is to attack it directly (as they're attached to the CT, which when destroyed means the 'mech is dead, anyway)
The tactical issue with the leg mounted weapons are that when you torso twist, the torso arc and the legs arc become different. What is more, they would make it very difficult to fire over terrain features, as partial cover from the legs up would absorb the shots (But on the plus side, you could shoot at targets under the water earlier, likely why the Hatamoto-Kaeru variant sports torpedo-launchers on the legs). Each weapon in Battletech, I imagine, are hooked up to some sort of actuator or ball turret of sorts to be aimed independently - especially in the torso locations, where getting the weapons to focus on a single location would be difficult. The main reason I have come to this conclusion is the comparison of weights between equal weapons found on both a 'mech and a suit of Battle Armor. Where a Medium Laser on a BA suit weighs 500 Kilograms, a 'mechs' medium laser weighs 1000Kg, or roughly double. My only assumption is that there must be a whole bunch of other mounts and actuators added to the weight of every weapon in order to give it that difference in weight.
So while aiming isn't going to be an issue, Terrain features and Torso facing would be.