
Originally Posted by
jmreagan
Correct. I've found the best way to line a rail up to the upper receiver; (at least on my Midwest Industries quad rails), is to take a removable carry handle and attached it to the receiver rail and the rail itself; half on the upper rail and half on the rail. Next, tighten it down well and then tighten the jamb nut down with the carry handle still attached. Finally I install the anti-rotation screw/pin last but don't crank it down too hard, just a hair past snug with blue locktite is sufficient. Remove the carry handle and boom; the rail is aligned as close as humanly possible.
To align newer M-Lok styled rails I align the barrel nut, gas tube, and upper receiver gas hole as close to perfect as possible. It usually takes 3-4 times of tightening, measuring, loosening, and retightening everything to get that gas tube in without binding at all on the sides of the teeth of the barrel nut while being aligned directly in the center of the receiver hole. Then I use the same process as described above with the carry handle for the final fine tune/rail alignment. It has worked every time for me with the most I've ever had to crank the rear site is 2-3 clicks in either direction to get zero'd. YMMV.
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