After testing many acrylic primers like Vallejo, AK 3rd gen, GSW etc., finally I found a very nice and smooth acrylic primer…which is actually paint 
I spray indoors, so I prefer the absence of smell and harmful vapors, though I have a spray booth. Mr. Finishing Surfacer 1500 is nice and smooth, but it is lacquer based. But now I found better alternative.
I initially bought this for painting the sides of my dioramas, because is very cheap-around 5EUR for 500ml in big bottle (price could be different in your place, but still is cheap)
It is Carbon black craft paint from Daily art, thick and creamy consistency, you can thin it with water and any acrylic thinner. It can be applied with brush, but I wanted to try it with the airbrush to see how it will work. I thinned with Ultimate thinner (water works also nicely) about 50:50 ratio and it sprays nicely through my 0.35mm HP-CS.
I was honestly surprised how smooth the surface it produced. Usually craft acrylic paints are not so smooth, because of the low price, but this is not the case. This is as smooth as Surfacer 1500 from Gunze, matte but not extremely flat, which is nice. It doesn’t obscure any details, as seen in this spare wing from Eduard Spitfire in 1/48. Dries very quick and is quite resistant even after 2-3 minutes of drying, but it is better to let it dry for 15-20 minutes just in case.
Not very easily to scratch with fingernail either, it will resist normal handling easily.
(Disclaimer: I’m not sponsored in any way, just bought this for my dioramas and found that is perfect for priming my models. I wanted to share this with you, if you want-test it, it is very affordable 
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