I don't think a full stun would be appropriate, but the static burst, target lock killing, etc. that the OP suggests is perfectly legit, and while annoying hardly a game breaker.
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Also make PPC's so you have to lead them,you shouldn't be able to hit a target moving sideways at range with lasers and ppc in one shot.
Why would you have to lead a target with a PPC? It's a lightning bolt, it moves at the speed of light. Unless we're playing at Aerotech ranges with 10,000+km ranges it will hit the target just as fast as a laser would. There will be a minute fraction of a second delay between when you pull the trigger and when the weapon actually fires, but that would have been calibrated into the targeting reticle already such that the weapon should essentially hit the exact spot your reticle was when you pulled the trigger. (of course, with your mech possibly being rocked by enemy fire and movement, that reticle might not be exactly where you wanted it to be) Even Gauss rifles will be essentially instantaneous travel over the ranges at which battletech happens. Modern Railguns have muzzle velocities of 5800m/s, assuming the Gauss Rifle (which admittedly, is a coilgun, which works on comparable principals) has similar performance it would take it about 1/5th of a second to cover its maximum range, which is faster than the average human reaction time (1/4 of a second).
Even Autocannons shouldn't have lead times, modern tank guns have muzzle velocities of 5500+m/s, and modern assault rifles run something like 4000m/s. At the <1km ranges that Battletech or Mechwarrior battles take place, the "lead time" needed for such weapons is again nearly non-existent, and can easily be hard coded into the targeting reticle.