Scope mounting height
by B.B. Pelletier
Before we dive into this subject, let me observe that last Friday's posting about the most popular postings to this blog has, itself, become one of the most popular posts! It has over 30 comments already, which is a record for such a short time.
Now, to business. This subject was suggested by DOT, who says, "I'm interested in mounting a scope on a rifle. One thing that does not seem to have been widely discussed is mounting height. If we do not want to remove the iron sights, is it best to go with rings that mount the scope higher so that our line of sight through the scope clears the iron sights? If mounted high, are there concerns about accuracy? If we mount it low, is there a shadow that is seen looking through the scope?"
From 357 Owner
We got such a good answer that I'm printing it here. "Dot, the issue of scope height is pretty much moot unless the iron sights are particularly high, or close to the scope bell. If either are the case, go high. Ghosting has never been an issue with the rifles I have scoped, but I have also never had one with large, high, or obtrusive sights. Accuracy should not be too much of a factor as long as it is sighted for a good medium working range. Practice at ranges used, and adjustment comes easy after a bit. Don't expect good results if you switch between 15 and 50 yards if you go for a high magnification. And don't plan on using the iron sights if you scope [your rifle], as even with high mounts it is a pain to use them effectivly with any speed. Not enough sight picture, and I think it messes with a part of your head switching between glass and iron with any rapidity. I've done my time behind a bit of glass, and iron, and do both well. But not at the same time." He said a lot there, but I would like to add my two cents.
For the CF-X guy
I gave a rather terse answer to the CF-X guy, who wants to scope his new CF-X with the lowest possible mounts. I have learned from experience, as 357 Owner also points out, that the height of the scope over the barrel really makes no difference to accuracy. The key, as he says, is to know your rifle and be familiar with it at the ranges you intend to shoot. Allow me to explain.
The "low-scope" crowd believes that, by getting the scope as close to the bore as possible, there will be less trajectory arc to deal with. This, they reason, makes for a flatter-shooting gun. In fact, it does not! Nothing you do with the sights makes one iota of difference to the drop of the pellet when it leaves the muzzle. The pellet begins dropping the moment it leaves the muzzle, and that drop increases rapidly as the pellet decelerates. Nothing optical can change that. The secret to a good air rifle sight picture is to select the optimum span of the trajectory within which the pellet arcs the least and gives what, essentially, looks like a zero that doesn't change. In other words, sight in for the first zero point at 20 yards, and the second zero point will be anywhere from 27 to 37 yards, depending on muzzle velocity and the pellet used. Caliber makes no difference in this determination, except that .22 pellets are usually slower than .177 pellets. Read more about the best zero points for an air rifle scope in the posting At what range should you zero your scope? and the follow-on to that post, More about sighting in.
You need a scope level!
The higher you mount a scope, the more you need to check level before every shot. B-Square, makes a great one that keeps you on an even keel for every shot. I like this model because it sticks out to the side, where I can see it without taking my eye off the target. The levels that ride the scope cannot be seen unless you move your head, which defeats the purpose of a level. That said, there is no scope that is so low that there isn't some possibility for canting error when sighting. You can struggle to mount your scope as low as possible, butyou'll still need a scope level, unless you get the scope somehow looking straight through the barrel of your rifle!
Do the open sights obscure the target when you use a scope?
Absolutely not. You can even mount a laser on top of your rifle in front of the scope, and you'll never know it's there. One thing about that...any object in the line of sight reduces the amount of light that comes through the scope. If there's too much stuff in the way, things can get dark!
A lower scope IS easier to see!
The new Leupold VX-L scope has a conformal cutout in the objective lens and bell to allow the lowest possible scope mounting. Leupold knows this doesn't make any real difference for accuracy. They tout the scope for lowering the exit pupil to allow the best spot-weld on the comb, while allowing a large objective lens for the best light transmission. This is the only real advantage such a scope gives. Another solution is to modify your existing stock so it fits your face properly. If stockmakers ever wake up, they'll start producing stocks that actually fit right to begin with. Most Theoben and Whiscombe rifles do, but they are the exceptions. This is a good reason to install an adjustable cheekpiece.
Leupold's new VX-L scope allows the lowest possible mounting for the best stock spot-weld.
You don't have to listen to me
Scope mounting is such a personal thing that you should do whatever suits you best. A lower scope is also no less accurate than a high one, so do what pleases you. After all, that's what airgunning is all about!