Chronos wrote:Actually it's wrong, at least in part. The copper actually acts as a lubricant. It reduces the drag or friction in the barrel. This reduces chamber pressures and that means less velocity. That's why you can increase the powder charge and have to to recover the lost velocity.
Chronos
Not really.
Copper is slipperier than lead but most handgun projectiles are coated in a very slippery paint as a lube which aids their travel down the bore with minimum leading and friction(as evidenced by recovered projectiles).
With copper wash projys the wash tends to drag the bore, they do feed slightly better(apparently, I never noticed any difference) but many copper washed projectiles are still waxed to avoid leading(think .22 or .22 magnum).
Both types generally obdurate well(expand and fill the bore- or engrave to the rifling).
The instance you are thinking of is copper washed steel projectiles such as in military ammo, in this case the copper's purpose is mainly anti corrosion but also a degree of lubrication.