I am trying to get some optics to use for a variety of heaters. I like the idea of quick detach mounts so I can spend more on nicer but fewer pieces glass or just switch between a long range scope and a red dot. I am confused about the manufacturer’s product lines in terms of specifying what the optic is for, i.e when they say a particular scope is for a shotgun or handgun, etc. Other than a scope designed for .22 not being able to handle recoil I don’t know why it matters. If a scope can handle the recoil of a centerfire cartridge I would think it would be able to handle a shotgun or magnum handgun. I think most handgun scopes would have relatively long eye relief but should be pretty strong if The Lord Humongous can use one on a Python to take out the radiator of a fleeing tanker. Would it be possible (or desirable?) to use a handgun scope with a scout mount on a centerfire?
First things first, a quick word from our favorite limey physicist.
The mutual forces of action and reaction between two bodies are equal, opposite and collinear.
For every action there is an equal but opposite reaction. Throwing lead one direction results in “recoil” in the opposite direction. This backwards force that we call recoil is what destroys scopes and wreaks havoc on unsuspecting shoulders.
Because recoil is a direct result of muzzle energy (the force of the bullet flying out of the barrel) we can use muzzle energy to compare rifle and pistol recoil. Wikipedia has a handy chart for just such an occasion.
At first blush it would appear that rifle recoil is significantly stiffer than handgun recoil, even the “varmint” 5.56 NATO round. But numbers can be deceiving when taken out of context. For anyone who has ever fired a .22lr handgun and rifle the difference is startling even with that mere 117 foot pounds of muzzle energy.
The killer of optics is sudden movement. With a rifle, not only is a lot of that energy “absorbed” by the weight of the gun (the momentum of the stationary gun cancels out some of the energy transferred) but the form factor makes the rifle much easier to control. While handguns only have the palms of your hand as a point of contact with your body, with a rifle you have a nice big stock and forward handguards to mold your body around. The length of the gun also gives you some mechanical advantage in controlling the recoil.
Thanks to that lack of controlled recoil even a small handgun round can absolutely wreck an unsuspecting optic. For this reason, optics destined for use on handguns are often “hardened” and over-engineered more than .50 BMG rifle optics. For that reason manufacturers specify which firearm optics are designed to be used on.
One other feature that sets handgun optics apart from normal riflescopes (and which you asked about in your question) is the “eye relief.” Normal riflescopes are designed to properly focus the image when your eye is an inch or two away from the scope, but handgun optics need to be held at arm’s length. For this reason the “eye relief,” or the distance from the end of the scope to your eye, is much larger. Eye relief is something that is defined by the designer of the scope when it is made in the factory and, unfortunately, is damn near impossible to change once the scope is finished.
There is a history (albeit brief) of long eye relief scopes being used on rifles. Typically, instead of mounting the scope on top of the receiver the mount is placed further down the barrel, allowing the shooter to still properly focus through the scope with their cheek on the stock. These types of rifles are often called “scout” rifles, a name coined by Jeff Cooper in the 1980s. The main benefit of scout setups are that the optic takes up less of the shooter’s field of view and gives them much better situational awareness than if all they could see was what was in the scope. It’s an interesting concept, and Ruger latched onto it this year with their Ruger Gunsite Scout Rifle that they released at SHOT 2011.
One last thing, about the swapping around of optics. If you move an optic off one gun and put it on another, or even just loosen the mounts and tighten them back up, chances are you’re going to screw up your zero. I published a review not too long ago about some mounts that won’t shift your zero when you take them off and put them back on, but that only works if you swap them around on the same gun.
Even a difference of 1/1,000th of an inch on the position of the barrel relative to the optic will mean the difference between being on or off the target, and generally no two guns are aligned the same. If you’re serious about moving optics between guns you might want to invest in a laser boresighter, as that will allow you to re-zero the optics so that they are more or less on paper without needing to fire a single round.
TL;DR: Handguns destroy optics better than .50 BMG rifles, Scout rifles use long eye relief optics very well, and swapping optics between different firearms will require the optic to be re-zeroed.
If you have a topic you want to see covered in a future “Ask Foghorn” segment, email [email protected].