I would suggest trying a variety(if you can find a variety in 16) of shells and see which ones work best for you. I used to use a 16ga 311 for my CAS shooting, I found that Federal made really nice hulls, but they wouldn't shuck out of the chambers easily. The black remingtons would fall out easy, though. Problem with the black Remington hulls is, the head is not brass, but brass colored steel, and can rust after loading with BP. Best to de-prime right away after BP so the primers don't rust in place. I didn't get many loads out of them before they burned beyond being able to reload.
For the Stevens, you might also think about brass hulls, but I have no experience with those.
Note: I haven't used my 16 for CAS for about 10 years, so the options may have changed.