I recently started using Bore Tech and have had good results with it. As for the copper fouling, like others have said enough shots and the shots will start to open up. Clean it, shoot a few fouler shots and it'll be good as new
It started as a hobby to feed my shooting and something to kill time during the winter months. It progressed into a lot of learning and wanting to increase accuracy.
Welcome to the rabbit-hole that is reloading. It's internal ballistics; if everything else is the same, seating the bullet deeper will result in less case volume which will in turn increase pressure and velocity. Likewise as ShtrRdy said, seating the bullet longer will get have less bullet...