AR bolt on frt sight issue ??? Help !!

[mjanko]

Ok all you AR gun smiths ..what is the secret to centering the bolt on YHM gas block/flip up frt sight for my AR?? I cannot seem to get it centered close enough to zero the rear sight ??? any and all help will be appreciated.

Matt

[Joeywhat]

Put the upper in a vice and level it...then level the gas block.