Author's Note: This is less of a full-fledged chapter, and more of a reply to a guest review.
Recoil behaves exactly as if the gun was not mass-lightened, which means it will behave as if the gun were firing its bullets much slower. A mass accelerator creates kinetic energy ex nihilo, as it works by vastly reducing the amount of energy needed to accelerate the bullet. Therefore an accelerator that accelerates its bullet at 3,364,000 m/s/s will only ever experience 67,280,000 newtons of recoil (large, but managable) (assuming a normally 20 kilogram slug) regardless of mass lightening. And remember, the more you mass lighten the gun both the faster the bullet comes out and the less time you need to deal with said recoil.