The copper bases, called gas checks, really aren't intended to reduce crud in the barrel. They are frequentlyused by handloaders pushing lead bullets. While it may have the side benefit of reducing stuff in the barrel, these are meant to stop "gas cutting" on lead bullets. There is a limit to how fast or hot you can push a lead bullet. At some point, the hot gasses and pressure from the powder overpower the lead and cut through the side of the bullet when loads get to be too hot. This results in poor accuracy and usually leading in the barrel. By putting gas checks on the base of a bullet, you can pump up the velocity of a lead projectile much higher, but still not as high as you can with a copper clad bullet.
Good luck
Hank