Unorthodox build advice

[Kluter Archring]

Okay, I've got another weird one. A friend of mine brings me a build consisting only of a race, his classes, and a concept, asking for advice on how to make it work, and I'm stumped.
So, what he wants, is a sniper. This already made me groan, because ranged characters have never been a favorite of mine. The real trick here, is that he wants to be a sniper as a half-elven shadowdancer (4 levels) and artificer (16 levels) Using the eberron Artificer (Found here: https://sites.google.com/site/eberronpathfinder/conversion-info/classes/art ificer )

His intention is to use a rifle, from the advanced firearms, and he wants to be able to one-shot one-kill things from as far away as possible, consistently. I'm frankly stumped, and don't want to come back to him empty handed. Anyone got any suggestions?

(As a note, he says that the build is largely flavor designed, the sniping thing was added on as an afterthought. He isn't planning on being great in combat, but he wants to be as good as this can allow)

Edit: As for content. Anything goes.

[SorrySleeping]

Are you the GM? Best thing I can say is Vital Strike. It is the closest thing to "snipe shot" the game has. Late game, he is never killed an enemy in one hit.

If you are the GM, you could give him super vital strike, adding more dice but removing later turns, or requiring a set-up (aiming). This poses the problem of being able to Target a big bad and just delete in a turn destroys party balance.

As someone that has GMed for, played with, and had another player use guns, they are the worst. There is nothing close to the sniper feel.

[Kluter Archring]

I'm not the GM, no, I'm not even in the campaign. I'm just usually good with some of the basics, but this goes a bit beyond my scope. I've found some stuff that people have found to let him do it- but it requires clas levels in stuff he doesn't want to take class levels in. So I'm trying to get as close as we can.

[The Sideromancer]

So, OHKOs are hard normally, and doubly so when you can't add a stat to damage. My solution is to get a wand of Named Bullet. As an advanced firearm, you'll be targeting touch AC for the first 400 feet, which is generally low enough for an easy 4* damage crit. Deadly Aim is a necessity here to crank up the damage, and consider Far Shot for long-distance engagements. Elemental burst enhancements to the gun would be useful, as well.

[Kluter Archring]

Oh, I hadn't seen Named Bullet, this'll be one to add to the ever growing list of stuff I send to hi. Thanks!

[JohnHawkins]

Named Bullet runs into serious problems particularly from a wand as more and more opponents get SR, also it needs time to use it or a known opponent if preparing in advance. I say this after players made extensive use of the spell in a campaign.
Also once the GM and the opponents are used to the spell high level opponents will often use Spell Immunity to remove the threat.

It is good but do not depend on it