Make sure if you use petstore corncob that it's either much smaller or much bigger than your necks...digging that stuff out really sucks...ask me how I know...
I quit with the corncob because it got in my primer pockets and I had to dig about 50% of them out with a tooth pick. I use the lizard litter now. It is like crushed walnut sand and works really well with the nufinish.