Back in the early 80’s, I was at the local rod and gun club range in Ft. Walton Beach Florida doing a little silhouette practice when a fellow showed up with one of the then new RWS Model 45 spring-piston air rifles. The Model 45 was the first  air rifle to claim 1000 fps. I noticed he had a very nice (read expensive) scope mounted on the gun.

     I just went about my business, but after about 15 minutes I heard this fellow swearing and cursing about how his new expensive airgun wouldn’t shoot no matter how carefully he held on the target. “Maybe it’s the scope” I offered. “It can’t be the scope” he replied. “It’s top of the line model, and it’s practically new. Besides, I use it on my 30-06 and it works fine.”  “It’s not an air gun scope?”  “No, why should I buy another scope for my air gun when I can use this one?” At that point he picked the gun up in disgust and rapidly swung it around to put it in his gun case. As he did so, a sound like glass rattling around inside a tin can could be clearly heard. “Hear that?” I asked. “Yah, what is it” he asked with a puzzled look.  “That’s your scope’s guts.” The poor fellow didn’t realize that powerful spring piston airguns could rip apart an ordinary rifle scope.

     To understand what was going on, we need to examine some basics about recoil and spring-piston air guns. First of all, it’s hard to imagine that an airgun would have any recoil at all. As we all know, with normal firearms recoil is generated by the bullet and gases exiting the muzzle. As you increase the weight and speed of the bullet and the speed and volume of the gases, recoil will increase. The only thing mitigating the recoil generated is the weight of the firearm. Heavier guns recoil less than light guns all other things being equal. All recoil is generated to the rear.

     On an airgun, a typical pellet will weigh only a minuscule 7.9 grains, and velocities are usually well below 900 fps on most rifles, and less than 500 fps on pistols. Spring-piston rifles and pistols are complicated, heavy mechanisms and consequently often weigh as much as a normal firearm, or more. For instance, my two RWS air rifles weigh 8, and 8.2 pounds each. Therefore you could reasonable expect the recoil generated in them should be absolutely negligible. With that in mind, how was it possible then for that fellow’s first quality rifle scope to be ripped apart?

     Well there are a couple of things happening here. First we have to realize that unlike regular firearms, 99.9999% of spring-piston recoil is NOT generated by the pellet and the air being expelled out of the muzzle. It’s actually being generated by the piston and spring, both of which are very heavy components, especially the large steel spring. When the sear is released, the highly compressed heavy spring will jump forward with tremendous force pushing the piston ahead of it. As the spring and piston are moving forward, the gun is recoiling back against your shoulder with significant pressure. Now here’s the part that many people don’t understand. As the piston comes to the end of the compression chamber it will actually strike the wall with substantial force, and the gun will now bounce forward, recoiling away from you.

     So the essential elements to be remembered here are that recoil from a spring-piston air gun is not light but actually fairly considerable, and that there are two recoil pulses in opposite directions i.e. one to the rear and one forward. For a scope to withstand the recoil pulse away from the shooter, it has to be constructed specifically for that task. Most scopes of that period were not.

     Ok, other than being constructed specifically to withstand a forward and rearward recoil pulse, what else distinguishes an air gun scope from a normal rifle scope? Actually the most important characteristic of an air gun scope these days is its ability to focus down to 10 meters parallax free. Ten meters is the standard distance that most air gun competitions are held.

     The key word here is parallax free. So what is parallax? As I explained in my series of articles on hand gun scopes earlier this last year, parallax is an optical condition in which the optical plane of the image and the optical plane of the crosshairs are not the same. The effect is that any little head movement on your part while looking through the scope will cause the apparent location of the target to move. In other words, when your head is in one location the target will appear to be in one place in relationship with the crosshairs, and if you move your head slightly, it will move to another location. On some poorly designed or constructed scopes the movement can easily be 18 inches.

     Rifle scopes without an adjustable objective lens on the front are engineered to be parallax free at 100 yards. When used at distances shorter or farther away than 100 yards, parallax will be introduced onto the image to some degree depending on the distance to the object being viewed.

     While some parallax induced target displacement is not a big deal when hunting most larger game, it is a very big deal when shooting groups, prairie dogs, or air gun silhouette targets, especially when standing. Even a single inch of parallax displacement caused by a slight shift in the position of your head or the position of the scope in relation to your head, can mean the difference between a hit or a miss on the tiny air silhouette targets - particularly the chickens.

     Well what about rifle scopes with an adjustable objective lens? Won’t that take care of the problem? The typical such scope will only adjust down to 50 yards. This means that they can’t focus or correct parallax closer  than that distance. Obviously being able to focus down to 50 yards doesn’t help us if we want to shoot at 10 meters.

     Additionally, there are also plenty of casual air gun scope users out there that prefer fixed power scopes with non-adjustable objective lenses. Hence, the manufacturers build special air gun scopes for that market.

     Now Bushnell is a different story. With the exception of two of their “economy” products, every one of their adjustable objective rifle scopes are mechanically capable of being used on a spring-piston air gun as well as being optically capable of providing parallax free viewing at ten meters. It is the only major scope manufacturer that I know that does this. This is absolutely amazing as it give the airgun customer a huge variety of scopes they can choose from as well having the flexibility of being able to mount their scope on either an airgun, or on to their favorite center fire rifle, or even a silhouette handgun. I consider this to be a major advantage. Hats off to Bushnell!

     Another issue that often comes up when discussing air and rifle scopes, is whether a specialized air gun scope (from any manufacturer) can be used on a regular firearm, either rim fire or center fire. If the air gun scope is equipped with an adjustable objective lens, in almost every case it definitely will allow the shooter to adjust focus and parallax from 10 meters out to infinity. Additionally, the robust construction features of these scopes allow them to be used on most firearms as well. Consequently I’ve successfully used  my air gun scopes on both rim fire rifles and pistols with perfect satisfaction. Additionally, I wouldn’t have any problem using an airgun scope made by any of the big three on a center fire rifle either. In fact I’ve done exactly that many times, using my Leupold 3 X 9 EFR scope (Extended Focal Range) on everything from a 22 Hornet up to a 30-06. However, I would be reluctant to use an airgun scope from a third tier manufacturer on a heavy recoiling firearm, although they would be probably fine for a rimfire gun.

     So getting back to the original question of “what is the difference between a rifle scope and an air gun scope?” The answer is “It really all depends on who the manufacturer is.” In the case of Bushnell there is essentially no difference between the two types. In the case of Burris and Leupold, there’s no difference in construction, but there is in optics. In the case of other manufacturers like Weaver, and Simmons, there is a definite difference in both construction and optics. For BSA, it’s a mixed bag. Some of their rifle scopes are mechanically compatible with air gun shooting and some aren't. However, none of their rifle scopes are optically compatible with air gun shooting. With Tasco, two of their rifle scopes are both mechanically and optically compatible with air gun shooting. They are the 8 X 40 X 56 Tactical scope and the Mag 40 6 X24. Interestingly, this particular Mag 40 scope is sold in the U.S. as a rifle scope and is sold in Europe as an airgun scope. The other scopes in the Mag 40 line do not meet either of the requirements for air gun shooting. Other Taco rifle scopes do meet the mechanical requirements but not the optical while even still others will correct parallax at 10 meters but not meet the mechanical requirements. You figure it out.

     So you see it's a very confusing situation. It’s enough to make your head hurt trying to figure out all these differences between the various manufacturers and even within a given manufacturer's line up.

     Last point. If you’re shooting a pneumatic air gun, the necessity for unique construction features for spring air guns becomes unimportant because there is no double recoil pulse. The main and only thing you need to be concerned about then is parallax displacement at ten meters. Fortunately there's plenty of high magnification rifle scopes around, especially from Bushnell, that will correct parallax at 10 meters.

     Moral of the story? Check those specifications in the company's catalog or web site carefully before you buy a scope for your airgun. If the specifications don't answer all your questions, call the company's tech customer service line.