I've tried all kinds of different ammo, but it doesn't help. I keep getting light indents. I've replaced the main spring, firing pin, etc, but no luck. I actually think it may be a lock up issue with the bolt, but don't want to spend the money on a new bolt to experiment.
Generally, I don't think lightening the hammer would work, most cases that would cause lighter strikes. But you may try drilling a hole and filling it with lead, to make it heavier. I'd try that but Ruger won't sell replacement hammers, because too many folks want to defeat the Mark III safety features with a Mark II hammer.