I've got some brass I had tumbled, necksized, and primed. Now I just bought a trimmer and full-length resizing die. So I'm thinking about resizing it and then trimming it. I would normally do this before priming it. What are you thoughts on doing it after priming it?

If you do it after priming, you need to deal with:

- Removing the depriming pin from your sizing die, so you don't pop out your new primers.
- Lubing the brass, and removing the lube, without damaging the primers.

Bottom line, sounds like a bad idea to me.

Oh I totally forgot about lubing and delubing the brass. Nevermind.

You'll only make that mistake once.

You can lube lightly and then just tumble the brass to remove the lube, it's no big deal and doesn't hurt the primers. Just make sure the breather hole in your size die isn't plugged, or it may pop out the primers by air pressure (depending on the die and cartridge of course)

Easiest way to lube for this (and any other sizing op) is to dump the cases in a ziploc bag and spray your lube in the bag (not directly on the cases), then zip closed and shake it all around. It doesn't take much lube to get a good even coating, and it eliminates the mess of those rolling pads. Some sort of aerosol spray lube is best, whether in a can or a pump sprayer.

Why do you feel the need to do that? You neck sized it to the Rifle chamber, did you then decide to run it through a SA Rifle?

Agreed, that would be the only real reason to FL size it. Otherwise just use it as-is.

Did you use a case gauge or check it in a chamber?

I was neck-sizing, but have decided to try out full-length sizing instead. The trimmer I bought trims based upon distance from the shoulder, so they need to be consistently full-length resized to get a consistent overall length.

I can either resize and trims these that are primed, or shoot all of them, and then resize and trim them.

If you are just shooting that brass in a bolt gun, don't FL resize it everytime. All you are doing is shortening the life of your brass and making more work for yourself.
Get a trimmer that Trims to OAL, and after doing it once you will likely never have to do it again for the life of the brass with a quality neck sizer.

If that brass was fired in the same rifle, then the shoulder position is already as consistent as it can be. If it was not all fired in the rifle you intend to use it in, you shouldn't have been neck sizing it anyway.