JT-AR-MG42 said:
...The collimator let a person check the zero on a rifle that had been sighted in.
The grid allowed one to make notation of where the crosshairs end up
(say, for instance, three lines below center and two lines to the left) on the sighted in rifle....
This is what the collimator does best compared to other "plain" bore sighter gadgets. For some precision fanatic (i.e. bench-resters) the use is like this:
1) Mount bases, rings, scope normally without loctite.
2) Shoot the gun & precisely zero the scope with your intended load.
3) Mark location of rings on scope with proper eye-relief & vertical alignment.
4) Use the collimator to carefully record the scope/bore zero.
5) Cradle the rifle. Tape the collimator in place & do not disturb.
6) Remove scope, rings & mount.
7) Epoxy bed the base then mount with loctite.
8) Attach bottom halves of rings to base with the proper torque.
9) Optically center scope reticle. (All elevation clicks divide by 2; Windage same.)
10) Place scope in ring halves & shim in place until reticle matches original zero of collimator.
11) Epoxy bed bottom of scope to rings. Let dry.
12) Epoxy bed tops. Let dry.
13) Add screws & Loctite rings.
The collimator is essential for this type of work, which is of little or no use to regular varmint or hunting rifles.
Just thought I'd add a FWIW here.