Ok i have read that if you change out the bobbed hammer on the USP Compact for a spurred hammer you could replace the hammer spring with a weaker hammer spring. The reasoning was that the spurred hammer weighs more so it hits harder.

The bobbed hammer weighs 'w' and need to go this velocity 'v' to hit with this force 'f' strong enough to ignite the primer.

The spurred hammer weighs more than the bobbed hammer. The velocity of the spurred hammer would have to be less to equal the same force.

Here is my problem, it would make take more force to move the spurred hammer to the correct velocity to get the right amount of force, right? So why would you replace it with a weaker spring?

I'm confused.

Thanks for your help guys.

Ignoring for the moment whether you can, or whether it's a good idea, here's one possible reason why, based on physics like you asked -

It's called the moment of inertia. Where weight is distributed on a rotating object can greatly affect it's moment of inertia, which determines how quickly it can be accelerated by a given force.

Here's the best example I can think of, and it is actually with a 100% weight difference from the light one to the heavy one -

Pick up an 8 lb sledge hammer by the handle, and hold it out horizontally from you. Now, as quickly as you can, swing it from your left side to your right side. Now take a 16 lb sledge hammer, but this time by the head, with the handle sticking out. Now swing it again. It will accelerate much faster and with much less force, even though it weighs twice as much.

As for your hammer question, it may either be incorrect information, or it might be true. Moment of inertia is just one possibility as to why.