Probably not a good idea. The hammer needs a certain amount of mass to generate enough force to dent the primer. No mass = no detonation.
eh...no. It's not momentum that ignites primers, but power
. All else equal, a lighter hammer travels faster and imparts more power to the primer.
Less momentum can make hammer travel easier to impede, though, so reliability can go down if
the hammer is too light and
the action is too rough and/or
springs are lightened too much. Otherwise, bobbing the hammer is a win-win - faster lock time and increased reliability.
BTW, I agree wholly with chaim: If you're going to fully bob the hammer, it's best to convert to true DAO by removing the SA notch on the hammer as well.