[Trexmaster]

I agree, the way it works now, Thunder Drive is practically unusable as in order to obtain it, you'd have to be firing with Safety on for two rounds, or spend the momentum on Charged Shot anyways (which is pointless when you could Overcharge for the same momentum and marginally more FP).

An alternative I could imagine is Thunder Drive activating -before- Charged Shot would, giving you Overcharge if you crit someone whilst you have Charged Shot, instead of having it spent before the check is made.

The OP's suggestion works just as well, and makes Thunder Drive far more usable, instead of simply a way of conserving FP.