I'm thinking about letting players overload there powdered weapons to shoot further. It would add <p> per every range increment beyond the listed one. Anyone think that's too powerful?

I would add a stress to allow such thing.

I would say that would also make a misfire much more likely, say reducing a 2 chaos star misfire to just 1 or something similar.

Like this maybe?

Over Charged Black Powder Weapons:

Gunpowder weapons may be overloaded to provide a more powerful charge. This is a dangerous game to play. A weapon firing above its powder capacity can be unpredictable at best. For each additional charge packed into a blackpowder weapon, apply the following:

• You may fire 1 range band further than the listed value.
• You must add an additional <P> to the weapons difficulty due to the powerful shot.
• The ‘Unreliable’ factor is reduced by 1. Weapons without an ‘Unreliable’ trait are treated as having ‘Unreliable 3’ and adjusted from there.
• Take 1 stress.

Note: All factors are cumulative. Firing a weapon charged with enough powder to take it below 'Unreliable 1' results in an automatic misfire.

For example, a weapon with ‘Unreliable 3’ that has 2 additional loads of powder packed into it would:
• Fire 2 range bands further
• Have a <PP> penalty to attacks
• Be considered to be ‘Unreliable 1’
• Cause 2 stress when fired

You must spend a manoeuvre to prepare and load the weapon before firing.