Yes everyone i get that there's no specific cartridge that does it all, i asked many question not just about calibers. That's only a small piece of the puzzle and i think we found it's spot. The consensus is 6.5, 300WM, and 338. Iv'e never considered 6.5 but with it's overwhelming response i'll start researching it, Thanks.
Now let's move on to other things, like overall shape, materials, barrel length, do you like guns with exposed barrel tops: example AI AWM. Or guns that are insides chassis: example CheyTac Intervention. Do you like rails? Where do you like them? Or maybe you prefer a streamlined design? etc etc etc. Anything other than caliber talk, this isn't a hypothetical scenario just an open discussion.
Sadly, 'caliber talk' is the most important factor, but not because 'one is better than the other' but because it specifically defines what the gun is intended for, which then drives all the other minor details that make it look cool & work well.
I'm sure it's been covered to death, but if the only criteria is accurate & lethal to an unarmored manimal at 1000yds, you only need a cartridge that's supersonic out to that distance --anything much heavier than a BB pellet at that velocity is serious bad news, regardless, and sonic flight means it'll be accurate. So something in the intermediate range like 223/etc with the right VLD bullet and healthy starting velocity (to flatten overall trajectory) would do fine. Supposedly those new 77gr 5.56 rounds can do this, and the various ~6mm AR-oriented chamberings do as well, as do the assorted super-short magnums. Even 308 is kind of overkill as far as recoil for such a role (which is where 6.5CM or 7mm-08 come in, though these are still more powerful than needed to be 'fatal' at longer range but excel at penetrating barriers, 300WM all the more so). Just something to consider, since less powerful rounds require less metal to contain the pressure, less stock/chassis strength to resist recoil, and less stiffness overall to resist smaller off-axis forces that cause barrel whip/etc. Snipers usually have to carry their stuff some distance, after all. Howa now makes a dedicated Grendel action that would make for a nice, light long-range rifle with a quality barrel & stock.
338LM is darn-near into anti-material range like 50 BMG, requiring both large guns and effective brakes to tame prodigious recoil. If killing Trans Ams at 1000yds is the goal, it's a better option than 6.5CM or Grendel.
The real problem with the word 'sniper' isn't that it describes a job/person rather than an object, but rather that the term itself is over broad. Snipers have a lot of jobs anymore, ranging from designated-marksman type stuff embedded in moving groups, to overwatch from a nearby position, to anti-material jobs on helicopters or generators, to surveillance/reconnaissance tasks that don't even require bullets, to the Hathcock ideal of stalking prey for days like a dirty wild animal behind enemy lines, to the Kyle ideal of stalking inferior prey like The Predator with the benefit of modern communications & weapons technology. And each of these has an offensive/defensive angle to them as well (sniping v countersniping). Originally, in the Hathcock days, the requirements were simple and in line with any good hunting rifle, but there's simply too many roles now for those guys for one rifle to do it all. Heck, I don't know much at all about these guys' jobs today, but I know they have a lot on their plate.
So the real question is what is the job, before what are the requirements for that job. Whether the gun is to be a 50lb anti-materiel behemoth fired from a stabilized helicopter or a lightweight patrol rifle with long range optic and accuracy is more basic than where rails are needed.
BTW, rails are
so 2010; O-lok is the new hotness today (is two more than M-Lok)
FWIW, my personal 'ideal' long range accuracy rifle is a modernized WA2000 in Grendel. A compact bullpup autoloader that's small enough for 'urban sniping' (or any place where a five-foot rifle is awkward, like everywhere), light enough to be carried for a spell & shot from the various positions (more entertaining than simple bench-rest or prone), still accurate and powerful enough to reach out to around 1000 yards effectively (good round number, and the farthest most can go without excessive practice, much more powerful cartridges, and massive telescopic sights & spotters, not to to mention well beyond the max range available to practically everyone). Also fully ambidextrous, possessing a quality match trigger, and sight mounting rail floated off both the barrel and its tension struts. The WA2000 was originally imagined as a purely anti-personnel rifle intended for counter-sniper/regular-sniper police activities that was small enough to comfortably operate indoors. Sadly, Walther made it
way too expensive, and also a lot more powerful than needed in 308, 300WM, and 7.5 Swiss, which made it bigger/heavier than would have otherwise been the case.
TCB
PS; rails are for attaching do-dads, so you want them for optics up top, and potentially for grips/supports on the bottom. You aren't attaching lasers or lights to the sides like a Costa'ed service rifle from five years ago, but just in case people insist there be some method to attach them there. The reason for a 'chassis tube' over the barrel is to get the point you can mount a bipod further away from the shooter (so the point of aim pivots less as the shooter moves the butt around) without having to attach it to the barrel directly & affect accuracy poorly.
