What kind of vest is it. Most of my team has the TT ammunition assault vest and I have to say its a great vest. Like all German gear its built to last. That flap is if you want to use the velcro or not. When its flipped over like in your picture you just use the buckles. Id suggest to tuck in the flap and use the velcro. It makes changing mags a bit quicker and makes sure you dont lose them.
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