Yes thinner paint is in order here, like MIkeV - many modelers generally start with a 2:1 thinning ratio. I too shoot Model Master flats for some projects and the 2:1 ratio seems to work great 90% of the time with my Badger 150 even with the Medium tip. The Med. tip seems to be better for our thicker modeling paints unlike artist inks and the like...where its thinner consistancy is better sprayed with the fine tip. It is possible to get fine lines with MM flats, I've tried the the following method with good results... I start by stirring the paint in-bottle followed by a good shaking. I ussually put a copper BB in the bottle which acts as an agitator to help thouroughly mix the vehicle with pigment. After a minute of shaking I carefully measure with my glass eye-droppers 2 parts paint and 1 part thinner (manufacturers brand). Added to this mix I add 5 to 6 drops of a paint medium called Oil Paint Medium (OPM). OPM contain D-limon oils and other ingredients which improves the flow of most oil-based, slightly increases drying time and glossiness. I stir the mix well and then strain it through cheese cloth, available at most home stores paint department advertised as "paint strainers". I am now ready to paint. Don't forget proper air-pressure! For this paint mix I usually set my compressor at around 10 psi. I load the color cup and test spray to check my results before going on to the model. I try to get a test spray line that is at least 1/16 inch wide to start with. With minor adjustments in air pressure you can get a consistant, finely atomized line of about 1/32 inch. Remember to stay patient, don't expect perfect results right at first, and just keep at it. The OPM will help trementdously so give it a try and good luck!
PS: OPM (Oil Paint Medium) is available at most good art stores made by Grummbacer and Windsor & Newton
Greg Williams
Owner/ Manager
Modern Hobbies LLC
Indianapolis, IN.
IPMS #44084