I remember doing the math behind the "distance" element a while ago.
A Cragtop Archer with a Dragonbone bow, with Farshot and Distance etc. Can make 1 attack as a full action ignoring penalties for shooting at extreme range. Some deepwood sniper added in helps with damage and synergises well. Glass of Distance allows you to see upto 10 miles.
The Pieces
4 levels in Cragtop Archer gets:
Strike From Above (Ex): Beginning at 2nd level, the cragtop archer gains a +2 bonus on damage rolls when making a ranged attack from higher ground than her target.
Arcing Shot (Ex): The cragtop archer of 3rd level and higher can fire a high, arcing shot to gain greater range with her projectile weapon. Any time the cragtop archer can fire a projectile weapon in an area with at least 40 feet of clearance between her position and the ceiling (or any other overhead obstruction, such as a forest canopy), her maximum range with the projectile weapon is fifteen range increments rather than the normal ten range increments.
Horizon Shot (Su): From 4th level on, the cragtop archer can seemingly hit targets as far away as the horizon as easily as she can hit something nearby. As a full-round action, the cragtop archer can make a single attack with a projectile weapon. This attack is made with no penalty for range, though it still has the same maximum range as a normal attack by the cragtop archer. This ability can be used in conjunction with any ability that extends the range of a projectile weapon, such as the Far Shot feat or the cragtop archer's arcing shot ability.
Cragtop Archer: +2 to damage, 15 range increments, no penalty for extreme range.
I used a Great Crossbow from Sword and Fist for the 150ft default range increment, but you could drop the range to 120 and go with the great crossbow from races of stone and trade up damage wise from 1d12 to 2d8. Or change to Greatbow, 120ft range, 1d10 but a x3 crit. I'm not sure if you could make Kaorti Bolts for a x4 crit...they're piercing... in which case the crossbow's better.
Dragonbone, increases range of a ranged weapon by 20ft, adds composite...which helps.
10 levels of Deepwood Sniper, enhances your criticals quite a lot, enhances range, poison use, rerolls... all good stuff.
Distance doubles range. Farshot increases range even further.
This puts us at a base range increment of 170ft, distance'd to 340ft, Far Shot'd to 510ft with an extra 100ft from deepwood. So 610ft. Hmmm That's only 9150ft, or 1.7 miles... my original was over double that but I forget how... anyway, it's within 10 miles so we can see through our "scope".
Kaorti Bolts would have a 16-20 critical for x5 damage. Which isn't terrible... we have poison use... could poison an arrow of slaying and add splitting to our bow. That means each shot forces 2 saves vs death and 2 saves vs poison which could easily be death.
We can also use the scope to teleport to the target and retrieve anything we need from the body.
I think I forgot ranged weapon mastery and flight arrows... also I'm not sure which order you apply all the multipliers and increases, I just know the extra 100ft from deepwood comes after farshot, as evidenced in the example given with the class.
I know this is a 1 shot 1 kill thread, but this was the closest I had to it, 1 shot, multiple saves vs death, works well with leadership for artificer of ammomaking (although what doesn't work well with leadership for an artificer?)