[mcguyver]

Likely, you do not have enough current capacity to drive the motor with that much load. Even with a new Magnum motor, you are going to need a shitload of current, likely 3000 mah is going to barely cut it.

When you double the output velocity of a gun, the spring requires at least 4 times the current to turn it over. This is in a "perfect world" scenario where inductive losses and resistive losses in a motor don't exist. In the real world, these losses can be extreme as you are coming very close to the design limits of this motor. In reality, you likely would need 6-8 times the current capacity of your battery to turn that motor.

Imagine taking a 4000 mah battery (big) and reducing it's capacity by 8 times. Do you think a stock gun at 300 fps will run very well on 500mah? Of course not. And even with 4000mah, you still need to factor in the instantaneous discharge rate of the battery in order to overcome the minimum in-rush current demands of a Magnum motor with an M170 (it's going to be big). Ni-cad batteries are generally better for this, but Ni-mh are not too shabby either, but generally the stated capacity needs to be alot bigger to make them as effective as the Ni-cad.