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Old January 5, 2013, 07:38 AM   #76
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
Some years ago, Ruger had problems with their receiver's not having barrel tenon axis well in line with their boltway. Other makes have sometimes had a receiver go out with the same problems.

Boresighting a bent barrel by looking through it then zeroing the sights on some down range point may not reveal its issue. Especially if it's only the last few inches of the bore that's bent. If the barrel is straight and both visual or muzzle-collimator boresighting ends up being way off from the scope's optical-mechanical axis, then the receiver's barrel tenon threads are crooked.

Note that putting a scope's adjustments at mid point in their range does not necessarily have them centered on the scope's optical-mechanical axis. That axis is typically off center of a scope's adjustment range. The only way to get a scope's reticule in line with its opto-mech axis, that is the center of the main tube front to back, is to put the scope in two fixed V blocks, one at each end of the tube, rotate the scope and make adjustments until the reticule center stays at the same place on the target as the scope's rotated through 360 degrees. That shows that as the scope's rotated, the image of the target where the reticule's centered doesn't move and therefore is exactly aligned with the scopes opto-mech axis. That axis is what the rings on the bases hold the scope at. And the amount of adjustment either side of that zero will typically be different both ways for both E and W knobs. Most folks are quite surprised at what they find out by doing this then checking the error between the bore axis and where the scope's axis is by boresighting.

So, check your mounted scope's alignment with the receiver with bases and rings attached only with the scope's adjustments set to the scope's true zero.
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