Do you mean the URBAN Gnasher, this was acquired by playing 15 games of CTL. if you did not play 15 or more games of this type during the beta you are Non eligible for this unlock.
if for any reason you feel you have completed this task your best bet would be to post in the forums for gears of war or try and contact the developer by navigating to their site here -->
someone from their can inform you how to get your weapon you have earned, or let you know that you did not earn it.
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