Janesy hit the nail on the head. I had my 870 Express jam on me on my upland hunt in Manitoba when a bunch of Hun's lifted off my gun jammed up. It took everything I had to open that dam chamber. I was shooting the cheap aluminum hull shells and the chamber was rough. I used a drill, cleaning rod with a 12ga brush wrapped in 0000 steel wool with some metal polish. Basically polished my chamber for about 3-5min and presto no more hang up's with the cheap shell. Give it a try, I know my uncle had the similar problem with his as well and they both shoot great.
Considering the price per 25 shell is 1$ more for the brass base, its 4 cents more per shell !!! there is limit to cheapness