AR 15 locking bolt lugs manufacturing question?

When manufacturing an AR 15 how do you measure the locking bolt lugs so that they align with the barrel when firing occurs? What i mean is how would you measure out your plans to create an AR 15 when you had reached the the process of mapping out the locking bolt lugs on the bolt so they align with the barrel... show more When manufacturing an AR 15 how do you measure the locking bolt lugs so that they align with the barrel when firing occurs?
What i mean is how would you measure out your plans to create an AR 15 when you had reached the the process of mapping out the locking bolt lugs on the bolt so they align with the barrel and....well LOCK!?!
I have looked at the AR for a while now and this part stumps me.

Heres a link to an animation of an AR 15 firing v
http://www.youtube.com/watch?v=FZipq6D6D9k&feature=related
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