Mounting and levelling a scope

I spotted this BSA 6-24X44 Tactical Rifle Scope on line around a week ago and it occurred to me that it might be a good scope for the Savage-Anschutz Model 10 rifle I purchased last year.  The Model 10 is a single shot .22 intended as an entry level bullseye rifle, but I purchased it as a rimfire benchrest and plinking gun, and that, along with my aging eyes,  means a scope is a must.  I've had good experiences in the past with BSA scopes on air rifles, and this scope looked like it might be a good choice for airgun field target or rimfire use. More on that in a later post. The first thing I do in mounting a scope on any firearm is to line the upper scope ring with a piece of electrical tape. This provides a high-friction surface that will grip without denting the scope tube.

 The next step, leveling the gun, is critical for accuracy. A scope that's not level is going to change the vertical point of impact as you adjust for windage, and vice versa. At 25 yards you might not notice the difference between just eyeballing it and using a level, but at 100 yards you definitely will. Many shooters just eyeball this, but I like to use a level, and not just any level. I have a very old Starret machinist's level of the sort used for setting up machinery. It's very sensitive to small movements, and will quickly reveal any misalignment:

The paint is well worn from decades of use, but the precision ground bottom is still flat to within a few thou:

With the gun clamped in a vice, find a flat spot on the gun to check for level. If your gun- like this one- doesn't have a horizontal surface, use the lower half of the rings as a reference. Once securely mounted to the gun they should establish a level platform.

Once you've established that the gun is level, place the scope in the rings and very loosely fit the upper rings halves. You don't want the scope to fall off, but you want to be able to easily adjust it.  The first adjustment is eye to scope distance- set this for the position you'll be shooting it.

Last, the most critical setting- making sure the scope is level with respect to the gun.

On most scopes, the best horizontal reference point is the top of the elevation adjustment knob or cap, and that's what I'm using here. As you can see, the bubble is just about perfectly centered. Turn the knob 180 degrees and check again. If you don't get the same reading, the cap isn't a level surface, you'll have to sight the scope at the range to finish leveling. If you do get the same reading in both positions, you should still double check it at the range for maximum accuracy.

Set up your rifle in a vice or stand at the range and using a level, set up a target with strong horizontal lines at 25 or 50 yards. Line up your crosshairs on the target, and check the level of your rifle. Still look good? You're done. But if you want the best possible accuracy, you'll need to shoot a few test targets. Zero your rifle at the selected range, and then shoot a few groups centered on the bullseye, and with enough left and right windage dialed in to get groups at either side of the bull. If everything is level, you've got your scope as level as you can.