I carry two spare magazines using a DeSantis double magazine pouch that has a flap on the back with two snaps that go behind the belt and snap at the bottom. It holds very securely and rides close to my body which helps with concealment. If you're a T-shirt kind of person, it's not the best option, you'd be better off with some type of IWB mag carrier. I go OWB the whole way around because I usually wear over sized printed button up shirts.
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USMC rule # 23 of gunfighting: Be polite, be professional, but have a plan to kill everyone you meet.
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