In the west, a “sniper rifle” is generally a precision rifle either selected for exception accuracy from service rifles, or specifically built to be used by a sniper. There is no requirement that a sniper rifle have any specific action or design, and so they come in all sorts of shapes, sizes, calibers, and intended uses. Despite this, an accurized AR-15 in 300 AAC has just as much legitimacy to the title of “sniper rifle” as a Barrett 50 cal or Remington M24. One nation even issued suppressed Ruger 10/22s for close in sniper missions. In the East…a sniper rifle generally looked like a “stretched out AK” or standard issue rifle with a scope slapped on, although purpose built military sniper rifles have shifted out of that mold.
So if a “sniper rifle” can run the entire range of rifles, from close range rimfire to ultra long range custom wildcats…is there a legally useful definition? No, nor is there even a good porn definition (aka “I’ll know it when I see it”). For example, the Steyr SSG 69, a dedicated “sniper rifle” looks and functions so similar to a Ruger American Predator that it is hard to tell them apart at a quick glance from a distance, and you certainly couldn’t tell them apart by group size or performance on coyotes.
Possibly a better question is “what ISN’T a sniper rifle?” and we can start to define that other rifles are built to purposes. A hunting rifle is a built and marketed for the taking of game (big, small, dangerous, etc). A competition rifle (Fullbore, Palma, smallbore, biathlon, silhouette, etc) is built for a given sport, generally putting holes in paper targets or knocking over steel targets. These rifles are built around the set of compromises for the activities of hunting or competing, and this parallels what we think of “sniper rifles” as being built (or modified) for competition grade accuracy in a hunting grade rugged system.
This is the same problem that Democrats had in the early 1990s when designing the “Assault Weapons Ban” which eventually decided on a basked of “naughty features” to define an “assault rifle” as opposed to any other rifle. Simply removing enough naughty features to comply with the law allowed domestic production of AR-15s and AR-10s to continue, to the dismay of Democrats who called compliance with the law a “loophole.” Of course any legal activity that they intended to make illegal that stayed legal with minimal compliance is always going to be a “loophole.”
I bring this up because there is not one thing, or basket of things, that when all added together equal a “sniper rifle” versus a hunting rifle or competition rifle. And this brings us to the bigger point, any legal restriction on “sniper rifles” would inherently be a ban on “hunting rifles” and “competition rifles” due to the fact that “hunting, sniping, and competing” are verbs, while “rifles” are nouns. What you do with a rifle determines whether it is a “sniper/hunting/competition” rifle or not. The cowboy action crowd has turned old school lever action rifles into competition rifles, even though they look like hunting rifles…. Anyone who claims they can write a law so precisely that it manages to make “sniper rifles” illegal but not “hunting rifles” or “competition rifles” illegal is either stupid or lying.