I always carry a single mag spare. I carry it on the left rear side(7-8 o'clock) as I shoot right handed. I keep the spare mag positioned in the mag carrier so when I reach for it it comes out so I can naturaly insert it directly into the gun. You never want to have to stop and see which direction the bullets are pointing. It wastes valueable time. You want to be able to, when your first mag is empty, drop it with your gun holding hand and at the same time be in the process of inserting the reserve mag with the other. whole thing should not take more that 3 seconds. (Reject, insert, rack) 1,2,3. My pistol holds 1 in the chamber and 17 in the mag, so I'm talking having 35 rounds readily available quickly.