How would you handle the number of guns an orgyn gunlogger can carry?

Just by carry weight? or would you say something like you can only carry 2 heavy weapons on you back in any way you can ready them?

Well, the game system doesn't take into account VOLUME when determining encumbrance. I usually am content to keep the abstraction going, but if it bothers you assume that excess heavy weapons beyond 1 or 2 have to be kept bundled and inaccessible in a pack on the Ogryn's back and aren't usable during combat.