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I recently purchased a laser bore sighter to get my scopes as close to optical center as possible using Burris signature zee rings and their offset inserts. Where should I set my scope when lasering at only 7 yds. and wanting a hundred yd. zero to start? My scopes reticles are 1- 17/32" and 1-11/16" above bore center. This is the farthest I can laser in my basement. Also I'm not quite sure where to put the offset inserts to make the corrections as I might be a little bit dyslexic .
First of all, you are not going to get a 100 yard zero with a 7 yard boresight.
Boresighting (and you may need the burris inserts to get a good boresight)will get you on paper and hopefully close, so you can then use a minimal amount of scope adjustments (and possibly additional or different burris zee ring inserts) to refine your sight picture to get a good zero.
At 7 yards from the barrel, the bullet is just beginning it's arc toward the target. Bullet drop is negligible (about 0.03"), so I would set your scope crosshairs to sight in above the laser dot on the target about 1/4 inch less than the distance of the center of the objective lens of the scope to the center of the bore. So if your distance between the barrel and scope objective lens center points is 1.5 inches, I would sight in the scope at about 1.25 inches above the laser dot at 7 yards.
For example, with a 150 grain 30 cal bullet and a muzzle velocity of 2900 fps, given a 100 yard zero, the bullet would impact the target at 7 yards 1.25 inches below the scope aim point if that scope were calibrated for a 100 yard zero and the objective were 1.5 inches above the rifle centerline.
That same rifle, with a scope whose objective lens center was 2 inches above bore centerline would impact 1.72 inches below a scope set for a 100 yard zero.
In both cases, the actual bullet drop would be about .03 inches (remember the rifle is actually pointing up so the bullet can arc through the air at the target.
There will be minor differences depending on bullet weight, muzzle velocity, and ballistic coefficient, but this should get you on paper at 100 yards.
As to your question about how to use the ring inserts. the rings are marked with numbers. Either 0, or -5, +5, -10, +10, -20, +20. the number signifies the number of thousandths of inches thicker (positive number) or less (negative number) the rings are compared to a zero (no offset) ring. You should use the rings in matched pairs.
How far this offset will move your scope depends on how far apart your scope mounts.
Using approximate values, if your rings are about 3.6 inches apart, each thousandth offset will move your scope about 1 minute of angle.
So if you are shooting 20 inches low at 100 yards, use a +20 and -20 insert pair in your front rings with the -20 insert centered in the direction you want to move your point of impact.
Conversely, if you are shooting 20 inches low at 100 yards, use a +20 and -20 insert pair in your rear rings with the -20 insert centered in the direction you want to move your point of impact.
This is a trial and error system. but by boresighting and using the burris ring inserts, you should cut down on the number of rounds it takes to get into the bullseye while not using up all your scope's full adjustment capability in the process.
Does that make sense? If not; if I have not been clear, please let me know.
thomae,
Thanks for the info. It will put me well on my way to getting this figured out.
My self only have 25 feet in my basement for using a bore sighter so i line up the cross hairs and make the i inch high there will always get on paper then get to the range and fire sighter's at 25 yards and adjust were needed
To simplify what I said earlier. If you sight in anywhere from about an inch to 2 inches above the laser dot at 7-10 yards, you ought to be somewhere on the paper at 100 yards. You really don't have to be as precise as I may have made it seem.
Enjoy! ;D