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I don't know about the other reviewers, however, my m4 profile 16-in barrel that I purchased on this site came with a dimpled gas block area to help align and maintain that alignment by providing better grip for the non clamping type of gas block with bottom set screws. Anyways, the dimple is not necessary to line up a gas block and it only helps provide extra security for gas blocks that use bottom set screws AND line up with the dimple, once the block is in it's mounting position, firmly pressed up against the gas block shoulder of the barrel. At this point, if your 2 or 3 set screws don't line up with the dimple, like many of mine in my past, it doesn't really serve a purpose and can actually lead to the gas block not being aligned with the gas hole on the barrel, which can cause a variety of issues.