When i get a magazine, new or used, I disassemble it and clean it.
Used magazines get cleaned, inside and out with a CLP, Hoppes #9 or whatever I have around. This includes the follower, base plate and spring.
New magazines just get wiped thoroughly with a dry cloth on the inside and the outside. This includes the base plate, follower and spring.
I then put two coats of paste wax on them, again, inside and outside. I also wax the base plate, follower and the spring (as best as I can). After wiping off the dried excess wax from all surfaces I buff all of the components and reassemble.
This works for blued, stainless, aluminum and plastic bullet feeders. Dirt doesn't stick to them and it provides some level of rust/corrosion protection. It is also cheap.