- Do you always add additive (Nu Finish, etc.) to the media?
I do. Just a little. What polish you add should theoretically last nearly forever. But the polish gets gunked up with brass and powder, so adding a little for each batch seems to work better for me.
- How long does the media last?
I'm working on "forever," with my controversial rinsing and reusing regimen. A batch of media starts to noticeably "slow down" after maybe 3-6 full tumbler loads, depending on how dirty the brass is and how long you leave them tumbling.
- Do you then rinse all brass to remove dust?
On my brass, the dust is trapped by the Nufinish. It transfers to your hand when you handle the ammo. I wear gloves while reloading, and I don't handle the ammo until I shoot it, and then I have to wash my hands, anyway. The only brass I rinse off is my rifle cases, after sizing, to wash off the lube. I use denatured alcohol for that.
- Tumble outside to minimize lead residue in the air?
This is a very good idea. Lead residue doesn't really hang in the air too long. But you don't want it settling on the floor in your house. In the reloading hobby, most cases of lead poisoning occur from ingestion, not inhalation. Some people tumble indoors with the lid on, but they only dump the brass outside. Some people tumble and separate their brass indoors, but I don't think that's a good idea. You'll know why after you look at your tumbler bowl after you've run a few batches.
Shoot, deprime, tumble, dry? What am I missing?
It certainly doesn't hurt to also wash off your brass before putting it in the tumbler. I shoot outdoors, so I use my media separator to get out the rocks and most of the dirt. Then I lower the separator into a bucket of water and swish around. Then take it out and shake out the excess water before dumping it in the tumbler.
Mineral spirits added each batch can help, too.
I don't personally see the sense of decapping before tumbling, but it's an option. It should reduce the amount of primer dust that ends up in your press's spent primer collection system. But it will increase the amount of primer dust in your media and potentially clog flash holes. After I size/decap, there always collects some primer dust in the bin of cases. If I have enough I might toss them around in my media separator for a bit to get out the majority of this dust before reloading. But usually, I just wipe the dust out of the bin once I'm done loading, and of course, I avoid handling the loaded ammo unless I need to, and never while eating.
Walnut is generally considered better at removing crud, but not as good at polishing. But you can always add polish to your walnut. As you can add mineral spirits to corn cob. So they both work. Which works better might depend on how dirty your brass is.
Never wash the brass as wet brass adds another days busy work drying it, and then you got those dreaded water spots
If you want to wash off the tumbler dust, I'd suggest you use denatured alcohol. Either straight, or cut with water. It'll dry quickly and leave no spotting. You can collect the cases with your media separator and put the solvent back in the jug for next time. Then take the cases and roll them in a paper towel, so any residue comes off instead of just drying in place. Another variant is to put a paper towel into the bottom of a metal bin and soak it with solvent. Then roll the cases around in it. Works very well for straight walled cases and you don't need to wipe them off or even wait for more than a minute for them to dry.
