Can copper BBS be fired in a pellet gun?

If the Owners instructions say BB's or Pellets can be used it would be OK. But IF the Owners manual says Pellets. Then NEVER use BB's in a pellet gun. Oh they will work. But you will ruin the rifling in the pellet gun or rifle.

Here is why. Good pellet guns have rifling in the barrel. (Little groves) that make the pellet spin as it is fired. Pellets have a soft skirt on the end that catches the air and conforms to these groves. This gives the pellet a spinning effect and adds to accuracy of the pellet.

BB guns have a smooth bore barrel ( Like a straw) the BB is hard and tumbles down the barrel and is not as accurate as pellets. If a BB is used in the Pellet barrel it slowly destroys the grooves in the rifled barrel. It also leaves residue from the copper in the barrel.

I've seen several good air rifles that have been ruined by the owner forcing it to shoot BB.

It's a poor idea to do this to a good air gun.