Try using the mag first. For a lot of setups it will work fine. Usually if you have problems it will be with bolt-over-bullet failure to feeds on the last 1-5 rounds in the magazine. My particular Rockr River 9mm upper would not strip the last 4 rounds out of any mag. The solution is the flatten the feed angle of the follower slightly so the round sits more horizontal. bend the follower legs with some pliers (GENTLY and SLOWLY, as the follwoers are brittle) until the angle is about halfway between what it originally was and horizontal, i.e. if the original follower angle makes the last round point up at a 15 degree angle, you want it to be at about a 7-8 degree angle when you are done.
It is MUCH simpler than it sounds, and once you find the proper angle it is easy to do to all the other mag followers.