let's start: firstly you must augment 2 hand weapon
then put that weapon on and u will get bonus like :+hp, +mp, +cp, +p atk and many others...
when you're equipped with 2 hand weapon put on a shield, then weapon will remove but stats are still added to your char .
you can have 2 hand guns as many as you want just all must put on you then shield again (gun; shield; gun; shield...) is work good job