Matching a scope to a centerfire rifle

Someone requested the scope info be moved from Gunsmithing to the Scope topic so I did a copy-and-paste on part of my post and of course had to add some new stuff.

Here are some guidelines that might help when selecting a scope for a hi-power rifle. The basic rule is to match the scope to the type of shooting you plan to do and to the usable range of the gun.

Basically there are two types of shooting requirements for high power rifles; hunting and target/varmint. The needs are radically different.

Here are some things to consider for a hunting scope:

Eye relief: The range of distance your eye must be from the lens to get a full view. The more powerful the magnification, the more narrow the eye relief gets. This makes it very difficult to shoulder the gun and find a view in the scope. At 4X you'll have at least 1.5" of eye relief range. This means your eye can be anywhere from 3.5 to 5" from the lens and still get a full view. At 12X, that narrows the range to about a 1/4" sweet spot. Your going to spend valuable time just trying to get your eye to find a view.

Field of view: As magnification increases, your field of view decreases. Field of view is rated by how wide an area can be seen at 100 yards. With a powerful scope, you will have a hard time locating your target because you can't see a large enough area. At closer ranges, all you see is hair and you won't know if you are aiming at the head or ass.

Light transmission: The more powerful the magnification, the less light is transmitted through the scope. To compensate for this, manufacturers use a large objective lens. Though it fixes one problem, it generates several more. The scope will be longer, heavier, and will require higher rings to clear the barrel. Higher rings move the scope farther above bore line so the trajectory doesn't track as well. Additionally, higher rings make the scope more sensitive to recoil and position the scope above normal eye level.

Parallax: With scopes 9X or less, the factory presets the parallax to 100-150 yards. With scopes 10X and more, parallax won't track so an AO ring is required. Parallax amounts to having the cross hairs in the proper focal plane. The more parallax is off, the more cross hair drift you get. The higher the magnification, the more parallax is affected. Clamp your gun in a vise and position the cross hairs on a target. As you move your eye up/down, left/right, you can actually see the cross hairs move on the target when the gun is totally stationary. When parallax is adjusted properly, you won't see any cross hair drift. If you get cross hair drift because your eye wasn't positioned exactly centered, your groups will drift and give the false indication of poor accuracy. When hunting, you usually don't have time to play with the AO ring to correct parallax.

Wiggle factor: The higher the magnification, the more wiggle you see and the harder it is to hold on target. For me, 4X is about the most I can handle without a rest.

Despite what you may read, most non-magnum rifles have a max quick kill range of 200-225 yards. Any shot beyond that is iffy at best. No doubt, deer and elk have been killed at considerably longer distances but more times than not, you will wound the animal and it will run off, never to be seen again. Using the standard of 1X per 25 yards, and a range of 225 yards, a 3-9X scope is just about perfect. I always keep my scope on the lowest X setting. If game is spotted at a long distance, you will have plenty of time to adjust the zoom ring. If something jumps up close, you don't have time to find the target in the scope, adjust the AO ring, play with the zoom ring, and take the safety off. You need to be ready for action immediately.

The most common mistake hunters make is to "over scope" their guns. Your hunting success rate will greatly improve if you stay away from high magnification scopes. I like a 2-7X or a 3-9X scope the best (3-9 is the most popular scope on the market). The magnification tells you a story; if the target is too small at max X, it is probably out of range for a quick kill shot.

Most target and varmint shooting is done from a rest where time is not critical. That means you have plenty time to get a good sight picture, adjust your zoom and AO ring, then get very stable on a sand bag. Here's where high magnification is more desirable. Yes, you still have the same issues as above but from a bench rest, they are much easier to deal with. Target rifles are more accurate than hunting rifles and are capable of small groups out to 300 yards or more. The general rule for magnification is 1X per 20 yards. Therefore, a 4.5-14X is one of the best power ranges for prairie dogs or punching paper up to 300 yards. Long range target shooters often go up to 8-24X or more.