Needle Size Discussion for Ammo Mig and Vallejo Mecha Acrylics Color

The key is going to be thinning and variations in application purposes. I can tell you that both paints will benefit from a little retarder in your thinner ( if you don't use a commercial thinner with retarder already in it) but especially the Ammo. I've shot Vallejo paints with a .25 but not tried the Ammo with that tip. I don't see why it wouldn't spray fine if properly thinned for the needle size and with retarder in the thinner ( some folks prefer flow aid but to me all paints get along with redarder and not all do with flow aid). No retarder and you will get an annoying amount of tip dry with acrylic paints but Ammo is exceptionally fast drying,  really with either needle, but it will show itself sooner with the small needle of course.

If you are not priming and clear coating from a rattle can and intend that to be part of your AB duties with your new AB you will need the .4 for those purposes anyway.

I am curious what airbrush you are using now?

I ask because if you have some airbrush experience and know exactly why you want the H&S Infinity, then all is well. If not, and you are like me and like to buy the best, maybe not so much.

I have almost bought the H&S Infinity 3 times over the past 5 years. It is a beautiful thing and the specs look so great. But I, like you, spray mostly acrylics and this is not an airbrush designed for acrylics. The small needle/nozzle sizes available and exceptionally small paint cup suggest same. You will find the trigger dead-stop adjustment useless for acrylics. Tip dries and the viscosiity of the paint in the cup also changes. I believe that detail airbrushes like this are designed for airbrush artists shooting inks, dyes, and watercolors. From what I've read, and to some degree from practical experience, the relatively large size of acrylic pigment sizes are not conducive to small airbrush needles. And from what I undertand, Vallejo (which is my most-used acrylic paint), is not among the finest of pigment sizes)

My point is, if this is a first airbrush and you are shooting acrylic, I'm afraid it will be a very frustrating learning curve.

I finally bought an Evolution 2-in-1 one because I wanted to have an H&S, and I basically never take the .4mm nozzle/needle out. Even it is probably overkill, but I sure can appreciate your desire to own and use an H&S.

There are lots of folk here with plenty more knowledge than I have, I hope they chime in to help you. And most of all, have fun in your research to buy!