Sniper rifles have been defined through history as meeting the following criteria, either been selected from amongst many issue service rifles as exceptionally accurate and adapted into service (Mosin-Nagant, SMLE, K98, 1903A4, M1C/D, M21/M25, Swede M41) or purposely built to serve as a snipers rifle (Druganov, M40, M24, M110, AI 96, Sako TRG).
I've written before about "sniper rifles" and my last post was about ammunition. Successful sniping operations are the sum of man, rifle, ammo. The most important part of the equation is the man, and the training that goes into making him (or her) successful. John Mosby wrote (and I paraphrase here) that people who focus on an equipment solution to a training problem are fools. He couldn't be more correct.
But in the vein of not handing a surgeon a meat cleaver, I'd like to address the rifle for a sniper. Bottom line, any rifle will do, depending on the mission you give him (or her). Accuracy is distant dependent, and a rifle that holds 4 inches at 100 meters can shoot out the eye of a sentry at 25. Even an AK with a red dot sight is perfectly adequate to shoot someone in the face at 25 meters. The Israelis used a suppressed Ruger 10/22 for such "close in" work.
The best sniper rifle is one that doesn't look like a sniper rifle, one that has the ballistics to do the job, and has the accuracy in combination with the ammunition to put that ballistic energy and momentum where it needs to go to destroy the target.
But since the standard for "sniper rifle" is a scoped, bolt action rifle, we will begin there. The standard sniper rifle is a 12 to 16 pound monstrosity with a very slow rate of fire and very distinctive profile. During infiltration and exfiltration the shooter doesn't carry this heavy bolt action rifle, the shooter carries something much more standard, like an M4 or an AK (or an L85 for the Brits, an AUG for the Aussies). In WWII German snipers would remove the scope from their Short Slide Side Rail mounted K98's until they reached their Final Firing Point.
Once at the FFP camouflage is improved, positions dug in (if necessary), range cards sketched, distances mapped, the rifle is put into position, the loophole carefully calculated. Iraqi "snipers" (and I use the term loosely) would often leave their sniper rifle in the final firing position. The point is, that up until this point, the rifle has been of very little use to the sniper.
If everything goes as planned, the sniper will take one single shot, and then exfiltrate out of the FFP, with no enemy the wiser where he was, or where the bullet came from. So you see, the sniper rifle has only a very small part to play in the overall mission, and for most of the mission it is dead weight. There you have it, humping in a monstrosity to take one shot then hump it out.
Now the Squad Designated Marksman, or Soviet Platoon Sniper, is a different role all together. Instead of separate missions, they become dedicated support to the organic maneuver force. Instead of deliberately prepared mission plans it becomes dedicated precision rifle support for targets of opportunity. Different mission, different tactical requirements. Only the Soviets put a doctrinal sniper rifle with the Platoon Sniper. Americans use M4s or M14s.