First of all, snipers are not suitable as standalone weapons. They need a secondary firearm, not only for melee oponents but also for all those kills where the enemy is good as dead and vs little pests like burrower spawns. A full 24 AP sniper hit is an overkill here.
Snipers kill from afar and kite pretty well but melee enemies WILL close in from time to time, be it from missing to hit, surprise/stealth attack, lack of ground to cover, loss of initiative roll or the need to dispatch someone more dangerous first. Once a melee enemy gets in his range you'll get precision penalties no matter what, because you need to either:
1.) Shoot while standing within melee range and suffer 40% or 25% (Spearhead frame) "close quarters" precision penalty (vs all enemies - not only those in melee range).
2.) Move away and suffer 30% or 15% (Spearhead frame) "move and shoot" precision penalty.
Those penalties are flat and can't be compensated by high guns skill. 95% CTH will always become 55%/65% or 70%/80% on a Spearhead sniper.
#2 will always apply and #1 can be lowered by 20% with the use of a
rifle barrel retractor, but if you need to waste a crafting slot for that, then there is no real use of a second sniper and it's much better to use a fast Assault Rifle as a secondary gun (11 AP 7.62 Hornet/RR 9mm Hornet/RR 8.6mm Chimera). ARs have 5% move and shoot penalty but none for close quarter melee range and ARs are DEADLY point-blank. Sniper has no use for DEX so naturally ARs are the best choice here but it does pay off to bring a 11 AP SMG along (ideally a smart, muzzled 5mm impala with shock rounds) vs situations where you're in danger of becoming
crippled.
And this is where some dodge skill is important. For a far-range build it doesn't have to be maxed out but it should be raised to at least 40 to qualify for
Uncanny Dodge, but @10 agility I'd raise it to 51 to make the effective dodge skill 90, which will result in a total of 5 automatically dodged melee attacks when activated. Can be increased further with gear but 5 attacks is usually solid vs single enemy.
Uncanny Dodge was nerfed a while ago and has a 5 round cooldown so it won't be a saver at all times. For this reason, like I mentioned above, it's good to have a SMG ready and equip it BEFORE encountering mobs with several unarmed or knife wielding enemies. On higher levels they're very likely to have the
Crippling Strike feat and stack the crippled debuff on hit. 1 stack alone lowers STR by 2 points and the character no longer meets the strength requirements to wield the sniper and AR without precision penalty. SMGs don't have any STR requirement so you won't have to worry about that.
Speaking of STR, most ARs need 6 but it's still better to leave STR at 5 and use rathound barbeque to get a temporary +1 buff. It lasts for 20 minutes which is plenty and it's never a problem to carry a dozen or so around. One base ability point saved is worth it.
On a low/0 armor penalty build it does pay off to max evasion, especially @ 10 AGI, actually on anything that can't rely on armor damage reduction and has at least 6 AGI. Nimble is good as useless without Evasion/Dodge.
10 AGI works very well with sniper ofcourse but the best reason to get it that high is the Blitz feat. Though it's awesome it's not nearly as important for snipers as compared to something like a x-bow character. The AP bonus from Blitz is capped to 20 AP so you end up with 70 AP but need 72 to fire 3 times with the anatomically aware rapid reloader sniper (24 AP). You could burst fire twice for 66 AP with the 11 AP assault riffle but that's not good enough, since the sniper is still your main weapon, and if it really gets rough you can still pop in an adrenaline shot. So I'd drop AGI to 8 to qualify for Uncanny Dodge, dump DEX, WILL, and yes, INT too, raise CON to 10 and put everything else into PER:
5/3/6++/10/10++++/3/3
http://underrail.info.tm/?build=AwGloJgVhGGYQA4QEZQoCwgQlcbhizJ4ykgBsMVR6+q9GA7NmfYR0SiBEthbG5QEUFlACclGEwRMsTaZPHigA
3 INT may seem very bad for crafting but actually you can still craft almost everything IF you make good use of Junkyard Surprise (+2 INT) and Core City home crafting bonus (+15% effective skill). With those two and only 3 INT, a maxed crafting skill goes up from 121 to 167 (at level 25). Search for those terms in the forum or Google if it's unfamiliar.
For a first playthrough I wouldn't worry too much about crafting. Just focus on Mechanics so you can craft a scoped sniper (you don't need the anatomically aware one until much later). Chemistry you need only if you want to craft special ammo for the AR (9mm acid and 8.6mm incendiary). 7.62mm micro sharpnel only needs Mechanics.
10 CON is not really needed but if you're still not familiar with the fairly complicated game mechanics, having a high hp pool and immunity to stun (Thick Skull) will save you alot of frustration later in the game).
I'm playing permadeath and by far most of the deaths were result of me getting stunned any not being able to mitgate the damage in the next round I had to sit out. If you don't mind even more min/maxing regarding the skill distribution you could try a slight different build. I play this one for permadeath, and I need to lower Chemistry (35 effective skill for 9mm acid rounds), a bit Mechanics can be saved too and some from Lockpicking/Hacking (70 effective skill is good enough for most common locks) in order to max out dodge. I repeat, don't neglect dodging melee if you rely on weapons which have a STR requirement.
AGI is lowered to 6 so no Uncanny Dodge but 16 PER at level 24 which more than compensates for the loss of bit stealth (and thus Snipe damage). It's more powerful and precise than the build I posted above so I'd encourage you to try it:
5/3/6/10/10++++++/3/3
http://underrail.info.tm/?build=AwGloJgVhGGYQDYQEZQuQhK43GVXQmHBAFgHYQyUD0J0iJMAOYuj-WiENuZKLSgIoVKAE4QFBBTJSYFSeNrjxQA
Uncanny Dodge is replaced by Rapid Fire so when you burstfire for 33 AP you can still fire 3 times for 16 AP with the 11 AP assault rifle (fits within 50 AP). In terms of overall damage gain it's even better than Blitz which has a 10 turn cooldown. RF has only 2. You should take it early unless you come across a rapid reloader crafting component, which you will use to get your 30 AP sniper down to 24 AP. In my experience it's not likely to be found before levels 12+ (when you're done with the drill parts quest).
Suppressive Fire is not a must-have, you can replace it with something of your liking. Survival Instincts, Evasive Maneuvers or Fast Metabolism are good alternatives.
