Commercial primer sealant is a cellulose acetate based compound in an evaporative solvent.
A form of this same compound can also be had in metal layout fluids such as Dykem.
I seal all my bulk 223 reloads with Dykem Steel Blue (or red if you so choose). Just a small drop from a syringe needle on the top of the primer, and it automatically flows around the entire crease before the solvent evaporates completely.
Works like a charm, and takes only a second per case to apply, literally.