Hello. I made a test with different sniper rifles to show you how ridiculously a lot it takes to take down one person. Snipers were: DMR .308, Savanna .308, Mosin 7.62x54, Scout 5.56x45, CR-527 7.62x39.
Distance - 375 meters, targets were NPC equipped with sweater, pants, desert camo plate carrier (standard vanilla), green Ballistic Helmet. They were located on Gliniska bridge, shooter was 375m away in S direction on the hill (look at the screenshot). No mods were used, only comminity onlite tools to spawn weapons and npc.

So, M14 DMR took 2 shots to the head or 4 to the body to drop a person
Savanna: 2 to the head / 4 to the body
Mosin: 2 to the head / 4 to the body
Scout: 2 to the head / 5 to the body
CR-527 2 to the head / 5 to the body

As you can see npc wears helmet+platecarrier, but sniper rifle should handle those. We have the sitiation where you need to land 1st shot is the head which is possible, but the 2nd shot in the head after person is alerted and moving/running/hiding is pure luck. 4 to the body - same, 1st - hit, after that: "nope, goodbuy, I'm outtha here". Even M14 DMR doesn't drop a player from 375m, and it has the highest bullet speed multiplier (1.23 as far as I remember). Even if not - Savanna not better. This makes sniper rifles not sniper, but CQB bolt action rifles. I'm not even talking about SSG with its 5.45x39mm, that one is extremely close cqb recomended rifle. 300-400m its the distance for Scout, CR-527 and SSG rifles, as those are cilivian/police sniper rifles, those shoud close this distance easily with 1 shot knock at least. And we have the situation where even DMR can't handle it. Savanna, Tundra and Mosin should cover at least 650m with 1 shot body knock, Savana and Tundra has 8x magnification scope for a reason, not just for peeping, otherwise simple binocular isn't worse. Right now if you have plate and helmet you can forget about snipers, which is sad, sniping is a very important (and cool) aspect in every such game, especially Dayz. I don't know what rifle you gonna add, but please don't add another .308/762x54, there's a lot of them and they're not that good as they should be. The game needs bigger caliber that can kill player with 1 shot to the body even on 800m no matter helmet/armor weared or not. I know you have your own vision of the game and your own plans, but think about this, it's impornant, sniping isn't in the best state in the the moment, it's in "barely OK" state. Think about it.