Mechs with arm-mounted weapons can choose to use both arms to help aim their weapons. The problem is that it requires the aiding arm to have all four arm actuators, they can only use the forward arc, blocks torso weapons, and cannot run/jump.
Fluff:
The Mechwarrior selects the weapon(s) on one arm and uses the actuators on the opposite arm to help aim it/them.
Game Rules:
- Using this aiming method gives a 1 pt bonus to-hit (maybe 2 pts bonus to-hit?).
- When using one arm to aid the other in aiming, the aiding arm must have all four different arm actuators intact (Shoulder, Upper Arm, Lower Arm, and Hand)
- Since both arms are being used, that means the weapon can only be aimed into the arc that both arms can cover, aka the front arc
- Since the arms are in front of the Mech, this will block all torso weapons from firing
- Since the aiding arm has to be locked in place, this option can only be selected/deselected at the end of the turn, after the Firing Phase (so if you take this option, it will affect your movement on the next turn)
- Since the aiding arm has to be locked in place, this also affects the maneuverability of the Mech. As a result, the Mech cannot move faster than Walk, and in addition takes a 2 pt Piloting penalty due to lack of flexibility in arm movement.
I'd see this primarily being used by Mechs that primarily have long-range weapons in one arm, as they can afford the lower flexibility caused by the Front arc limitation and don't have to worry about blocking torso-mounted weapons.
Likely to use:
- Panther w/PPC
- Phoenix Hawk w/ LL
- Thunderbolt with LL
Not likely to use:
- Stinger/Wasp w/ ML (too short a range to accept limitation)
- Daishi/Dire Wolf (no hand actuators)
- Archer w/ML (too short a range and will block torso LRM-20s)
Got the idea from seeing the various Transformers and Robotech movies where the Mecha would hold and fire the gun with one arm and brace it with the other.