For handgun brass being sized in carbide dies, I just tumble in media with NuFinish added. It significantly reduces the sizing effort as compared with just clean brass.
For rifle brass I roll them on a paper shop towel with some Castrol Synthetic motor oil. I also polish the interior of my sizing dies with Flitz. The synthetic oil is quick to apply, makes sizing easy, and comes off quickly when tumbled in media with some OMS (odorless mineral spirits) added.
Prior to converting to synthetic motor oil I used:
- original RCBS sizing lube applied on the RCBS pad. Lubed well, but easy to get too much on and dent case necks. Messy to remove
- Lee sizing lube. Harder to apply evenly, easy to remove, can rust your dies since it is water based. A very good lube. My understanding is this is used in commercial brass drawing processes.
- Imperial sizing wax. Great lube, low sizing effort but way too slow to apply for me.
I can size 750 rounds per hour, lubing, sizing, inspecting when using synthetic oil. It doesn't take much and if you miss a case it sizes just fine. I decided to give it a try after seeing a YouTube video where a guy was using it. I am probably willing to try anything, but just really like how well it works for me. No dents, no stuck cases, no time limit. I just read too may posts about folks sticking cases with spray on lubes.