Adjusting For Scope Height
When deciding on how high to mount a rifle scope, in most cases the basic low rings and bases will get the job done on firearms that use glass sights.
However, when the scope changes from the smaller bell sizes to the larger target or longer-range models then yes, there is a need to upgrade the scope bases and mounts to increase the necessary clearance for the barrel, or at times when there is an extended rail pre-mounted to the rifle's receiver or fore end tube housing.
In some cases, the manufacturer of a scope will indicate in the mounting directions exactly what height of base ring system is required. When scopes go up to the 50-inch bell size, the rings needed are, in general, about medium high. But larger scopes require higher rings.
While not addressing a specific scope, it is difficult to determine exactly what scope ring height is required.
Also to be considered is the tube size on the scope. Many times the larger “big rifle” scopes use 30mm tubes through 33mm tubes. This means that the scope tube will contribute to the actual distance that is required between the bell lower edge and the barrel.
As rifle scopes become more specialized, so the sizes keep increasing. Once you're into high scope mount systems, you must also check out the height of the butt-stock comb. You will have to "chicken-neck" to get into the scope if your stock comb is too low.
Current mounts, such as one-piece mercantile mounts, are often sized at the higher end of the scale. I have found them to fit most needs, even when using 50mm scope tube bell sizes.
Even then the new super long-distance rifles use special adjustable MOA bases, and special scope rings that can also be moved up and down are in a class by themselves. If you're shooting at that performance level, you're most likely well-informed regarding your equipment needs anyway.
Assuming you're all set with the correct height of your scope bases and rings, the next thing you may want to do is get the correct height of the actual scope. This information will be used when working through ballistics calculations for long-distance shooting. It has little value, however, when undertaking normal range shooting.
In most cases, ballistics firing solutions are factored with the scope measured, or at least guessed to be, 1½ inches from the center line of the bore. If you require exact measurements, set the scope in a level vice (gunsmith-type) and measure from the dead center of the scope reticle to the center of the bore.
In the event you need to change the exact position of the reticle center, the new position will also need to be corrected when you build the next set of ballistics data.
Remember, all of this detailed data is part of measuring the first round hit on a target 1000 yards through one mile away, or more. If in doubt, or if you can’t measure the distance between the scope center and the bore, just assume 1½ inches and get a good night's sleep.
More often than not. a long-range set-up can mount a scope that has a center-to-center measurement of 3 inches or more. That's nuts in terms of angle, but it's required if standard optical systems are being used for one mile through current shooting this year of three miles.
Yes, that is correct. Three-mile shots are currently being attempted against the backdrop of special landscape situations.