iirc someone calculated out how much recoil a gauss rifle would generate compared to the average weight of mechs that field them. It was significant enough that I think they should (at the least) cause a sudden slow down, if you fire them while running forward. If you fired them while going backward at top speed it might even be enough to topple your mech. (especially if multiple were fired at the same time, or if you had other poor conditions like firing up hill while on a slope)
20-100 tons is a lot of mass to move, but with the ridiculous speeds that GR create in their 125kg projectile.... there's a -lot- of recoil.
As far as AC vs. GR in terms of recoil GR's are way higher because: F (recoil in this case) = M (mass of the projectile) * A (acceleration of the projectile)
1. their shell is a solid slug. More mass per round.
2. They generate far more acceleration than an AC round (ac rounds do their damage by exploding when they hit the target. Gauss rounds do their damage by being a large chunk of metal flying at insane speeds)
As was previously mentioned, Gauss rifle rounds wouldn't accelerate any slower than an AC round, most likely. Granted, they do their acceleration over the course of the entire barrel, but guns of today do this as well. Propellant does not burn instantaneously. Plus, Gauss rounds have to get to a much higher speed than AC rounds would, so they would likely have higher acceleration.
Edit: One example of how guns are not instantaneous in their acceleration is taking the same round and firing it in a different barrel. (ex: pistols generally have lower muzzle velocities than pistol chambered carbines[aka rifles that use pistol amunition]) If acceleration was instantaneous, muzzle velocity would be the same, no matter the length of the barrel. It's not, because the bullet has a very compressed pocket of gas behind it (created in the explosion) that continues to push the bullet throughout the barrel. If your barrel is the perfect length, then the gas pocket will continue to accelerate the bullet up to when it leaves the barrel.
This is also why bolt action rifles have more muzzle velocity, and are better for long ranges. Semi auto guns usually funnel off some of the gas from the bullet in order to operate the action and chamber the next round, whereas a bolt action rifle uses all of the gas to propel the bullet, and then has the user manually chamber the next round.
Edited by LackofCertainty, 14 May 2012 - 04:59 AM.