OK to use.
Absolutely ok to use but just to be clear, if you are planning on shooting your Glock in the Production category, you can only load 10 rounds into any magazine. If you wish to fill your magazines, you would need to choose to compete in either the Limited category (against other shooters who either wish to load to capacity, or may be using an optical sight), or Open category (not many contestants usually, but those that do are usually running a very high speed, low drag blaster). Alternatively, there's enough folks running Glocks that you almost certainly borrow a mag or two without a problem. Just speak up in the FNS thread a day or so ahead of time.
ok so i am trying to get enough stuff to participate in Fns. My G19 will be my primary comp gun. do they allow us to use a 33 round mag. i only have 3 reg. g19 mags but i do have a 33rd mag that could supplement the two mags i dont have. just thought i would ask. Thanks everyone.