I've done a little research on this issue...
on airgun scopes:
On PCP rifles (pre-charged pneumatics), or PUP rifles (pump up pneumatics), it doesn't matter - a rifle scope is fine.
BUT, on *spring piston* or the new 'gas piston' guns, particularly powerful ones, it can matter and these can destroy certain scopes' reticles very quickly, because the recoil is so-called "2-way" recoil instead of one-way recoil like firearms and PCP or PUP guns. On a firearm or PCP airgun, the recoil is 1-way - backward (an equal and opposite reaction to the bullet leaving the barrel). Even though it may be very powerful backward, it is only backward. OTOH, a spring piston airgun recoils in two directions...first, it recoils backwards like a rifle. Then, when the piston reaches the front of the cylinder, and stops, the inertia makes then gun the 'recoil' forward - secondary recoil. The problem with this situation arises when a scope's reticle is not supported on both sides. If it's supported solely on front side, this protects it from loosening/breaking from backward recoil. But if it's not supported by glass on the rear side (or just a heavy-duty, well-secured reticle), then this forward recoil will jar it and possibly disintegrate it. So, it's usually a safer bet to get a scope designated as being for an airgun; then you know the manufacturer has either made the reticle heavy-duty or supported it on both sides. Having said that, ALL Leupolds (all lines), and ALL Burrises are supposed to stand up to spring piston recoil, and I believe they put that in writing. In addition, all Bushnells Trophy & up are supposed to take the abuse as well (i.e. Trophy, Legend, and the Elites, but not the Sportsman, Sportview, or Banner). These 3 makers have certain models designated as airgun scopes, but ALL of them will be covered by their warranty if broken by a springer, if they otherwise have a warranty, even those not designated as airgun. Also, supposedly, the Swift Premiers are supposed to handle it. Also, BSA and Simmons both have a few scopes designated as airgun, as well as a couple other makers. Also, Nikon told my by telephone that ALL of their scopes will stand up to springer airgun recoil, but it's not specifically written anywhere that I can find such as their website, so I'm not sure if I'd trust this 100%. BUT, in reality, the OVERALL strength of a maker's warranty service in general is going to be far more important than whether you have to argue with them about whether you voided the warranty by putting it on a springer. Therefore, it is never a mistake to go Leupold on an airgun, since their warranty is so darned good, on all their lines. Ditto with any other makers with a super strong warranty because (a) the existence of a strong warranty reputation means that their scopes are going to be generally well-constructed, and thus less likely to break even if not specifically designed for an airgun, and (b) they'll just flatout give good quick service if you break it, no questions asked.
Now, all that has to do with scope construction/design. In addition, you will almost always want to get an AO scope for your airgun of any type, so that you can eliminate parallax at close range; which is why most (but not all) airgun-designated scopes have AO on them. I've used Burris and Bushnells with AOs on mine (and 1 BSA), and so far no problems - I cannot afford the Leupolds with AO, but if I could, that's what I'd get. Bushnell Elite 3200s and 4200s with AO are a real good value for springers, because they have a pretty solid warranty & construction.
