If by 'bullets' you mean loaded ammo, there used to be a few places on line you could use your spent brass as a credit to your reloaded ammo purchases. They may still be around.I don't get why no one has set up a home business where people give them spent brass and get bullets at a cheaper price. Seems like it could be a win for everyone involved? Of course, I don't have the know how or the equipment to do this..
As far as shooting some one else's reload, proceed with caution.
To obtain an ammo manufactures FFL, pay for insurance and other business expenses, it seems to me that one would need to have a significant volume to make it worth the hassle.