How do I think acrilics for my airgun?

I've been using Model Master Acrylics here lately, and i've found that just using water for thinning has worked best for me.

I'm using Modeler Masters acrylics. Would Isopropyl still work?

Ross has one of the more accepted methods of thinning acrylics, I also use Tamiya and haven't had any problems using water for thinning. The amount that I thin the paint is based solely on the characteristics of each colour, some are thin enough already. It should have the consistency of milk for the best results.

Depends on the brand. Of course, the manufacturer's proprietary solvent always works. There was also an article awhile back in FSM that had a table. Might be out of date if formulations have changed. (They do, with often frightening rapidity...)

Polyscale: water
Tamiya: 90% isopropyl works best for me.