Legality of it? Not sure. I do think that carrying two riflesthe wayyoustated might get you the kind of attention that would keep you out of the service. If it were me, I would put them in cases or range bags and carry them that way.
Actually, if it were really me I would get my exercise some other way and drive to the range. :P
Or you could go extreme sniper and lowcrawl the entire way, dragging your bag behind you. 12 hours to get there, take your shot and 12 hours back. Repeat.