Scope Alignment Question

[Coltdriver]

I have mounted a 3X9 40 scope on my 30 06.

Midway had this neat pair of bubble levels that you mount on the scope adjustment cap and then put one on the receiver and that you match the bubble centers as you tighten the scope into the rings. Worked great, I am very happy that I have the cross hairs absolutely perfect.

Heres the set up to my question. I have a pair of Leupold rings. The front ring swivels into a dove tail. No variability there.

The back ring has adjustments screws that let you cinch each screw against a set which in turn wedges the set under a partial cut on each side of the receiver mount.

The problem is getting this setting exactly centered so that the scope line of sight is perfectly parallel to the barrel.

Lets assume that I get this within a 32nd of exactly centered.

When I adjust the scope for left or right bullet impact does my actual line of sight through the scope cross hairs then parallel the barrel? Or would I find that I was spot on at 100 yards and then find the bullet off to the left or right at 200 yards??

 

[browningguy]

At 1/32" I wouldn't worry about it, at any range you are shooting the grouping ability of the gun and shooter will outweigh such a minor alignment issue. You are correct though in that there will be some error.

 

[dmazur]

I believe that the reticle adjustments (turret) determine line of sight, and the scope mounts determine how parallel the scope body is to the barrel axis.

Unless the scope mounts are way out of parallel, the reticle adjustments can normally zero the scope correctly.

I'd borrow (or buy) a laser bore-sighter and use it to get things centered.

With the scope reticle centered (count total clicks from one stop to another, then go back half way...both L/R and U/D), use the Leupold rear screws to get the reticle above the laser dot. Probably at 25 yds or so.

As the scope is typically 1-1/2" above the bore, the laser dot probably won't be coincident with the reticle at close distances. It should be below the reticle. However, as you are concerned with L/R mount adjustment, just get the reticle directly above the dot.

After you get the mount screws set according to specs, leave them alone. Then proceed with a normal scope zeroing procedure at, say, 100 or 200 yds.

(As far as I know, the only problem with having mounts way out of alignment is that you can run out of reticle adjustment before you get a correct zero.)

 

[sacp81170a]

If your rings are out of alignment by that much, you can get an alignment kit from Midway or Brownell's. Better yet, get a ring lapping kit of the appropriate size (30mm or 1") and follow the instructions to lap your rings so they fit the scope without putting torque on it. The lapping kit will pretty much align your rings, since the blank used to do the lapping is a solid piece of steel. The advantage of the alignment kit is that you can check how the rings are lined up with the bore, but if the holes for your mount are drilled and tapped properly you should be close enough to be well within the adjustment capabilities of your scope.

You don't say what your purpose is in mounting the scope, whether you're hunting or long range target shooting. That will determine how precise you need to be in mounting your scope, although only you can determine how much time and money you want to put in it. Hunting, minute of deer is good enough. High power or bench rest matches, nothing will ever be quite "good enough".

 

[dmazur]

Just trying to help, not argue. The OP has a Leupold mount, which has a swiveling dovetail in front and a windage adjustable mount in the rear. No torque. No need to lap rings. He appears to be concerned about aligning the rear mount so the scope is parallel with the bore.

I believe the way this mounting system works is that you adjust the rear mount so the scope is more or less parallel with the barrel. Some people just eyeball it. I recommended a laser boresight so it can be better than that.

At this point, the user should leave the rear mount alone. (Tightened to be essentially permanent) Proceed to a scope zeroing process.

By zeroing the scope after adjusting the rear mount, there will be no L/R error, regardless of range. I think this answers the original concern.

 

[Zak Smith]

If you had a 1/10th error left to right -- ie, the scope center was 1/10th to one side of the barrel axis - then you'd see only a 1" error contributed at 1000 yards if you had a 100-yard zero.