For those that use a sanding sealer what grit do i sand it to ?

Jim,

What sanding sealer did you use? 

On my "E" model, ARGO, I used Deft semi-gloss on bare wood because it's lacquer based, then followed by layers of Minwax water base Polycrylic.

I sanded that with 320 before applying a thin layer of primer, just enough to cover. 400 on the primer and quite a bit has been removed. 600 on open bays.

Well the only sanding sealer I could find is what I am using.
Cabot quick dry sanding sealer, clear satin finish.

seems to fill the grain easy enough. Just not sure how fine I need to go before using poly on top.

Jim,

It must be lacquer based, correct?

Jim, I'm currently using the cabots as well, and the rep said it's basically identical to polycryllic.
So, i personally sand it with 220 and then 400. 400 is what i use before the color coats of rustoleum. Works for me with no grain showing, so long as the prep is done.

Yes sir, we must be talking about two different products they have. This is the one i use. I like water based products in certain applications because i mix corn starch in this stuff. Works great as a sanding sealer.

lacquers are usually shellac, acrylic, nitrate(dope), butyrate(dope),  with various acetates or ketones plus xylene and toluene solvents.

Vinyl and hydrocarbon resin, along with naptha, xylene and ethylbenzene are more like varnishes.

Varnishes and enamels use various kinds of alkyd resins and oils that will cure from oxygen in the air dissolved in mostly mineral spirits solvents.

Mostly lacquer is a name for a hard, sandable, solvent resistant clear finish.  Polycrylic finishes usually are very hard and brittle, but sandable.  They tend to raise the grain on raw balsa  so a couple of coats of nitrate dope are needed to keep the wood smooth.

The zinc stearate bridges small gaps to keep the finish from soaking in too much and makes it more sandable.