I always tumble my brass in walnut first, followed by corn cob, with a bit of NuFinish both times.
Last week, I was setting up for the corn cob polush, and couldn't find the NuFinish! Looking around the shop, I found a container of 'Mother's Plastic Polish', and decided to try it. The cases came out looking better than with NuFinish! This was after about two hours in the corn cob.
I suspect that the plastic polish has a finer grit abrasive, hence the brighter, mirror-like shine. Oh, the plastic polish is also great for rejuvenating your platic shooting/sunglasses.
Has anyone else tried Mother's for case polishing?