Danish oil is what's called a 'wiping varnish', and it's a mixture of an oil (tung or linseed), some mineral spirits, and some varnish. It's an oil finish, so you can put a standard or a spar varnish over it. Personally, I don't see the need for a spar varnish in a gunstock application. Minwax Fast Drying Polyurethane, either brushed or sprayed, looks great and dries fast. You can get it in gloss, semigloss, or satin. I prefer the satin for gunstocks, but that's just me.
That said, I'm a woodworker (call me a good amateur), but I do know a fellow that is a true professional. He has just 'adjusted' my thinking on wood finishes and I'm trying his approach out on a project I'm doing in Cherry. What he suggests is that, after sanding to 400 or 600 grit and raising the grain a time or two to remove the 'whiskers' that result, you apply one coat of Danish Oil as a primer coat. For your needs, you might want a colored Danish Oil, but I'm using the Original in clear. After that, he suggests up to 4 coats of Waterlox Original in Satin finish, wet sanding with wet/dry 600 grit sandpaper as each coat is applied. Treat the Waterlox as a wiping varnish and wipe off the excess at each application after you've given it time to soak in. I've tried this approach out on a scrap piece of Cherry and the finish is amazing (smooth as marble). For my particular project, I'm going to stain the wood with a water based medium cherry stain after the grain raising and before the first coat of Danish Oil.