On planes that have two standard gun sets, like the P51D, the select weapon will switch the primary from the single inboard .50s to the outboard dual .50s and it makes the single inboard .50s the secondary gun.
However, when I do that I also get VERY WEIRD results, like rapid ammo loss, frame rate jumps and jitters, sound irregularities and such things.
So, I treat it like kissing your sister. I avoid it at all costs
[ Not to say anything about YOUR sister, that is referenced to kissing ones own sister in general. ]
fuzeman
I think it's kind of like your appendix too, obsolete, and you only notice it when it gives you trouble.