I call this build "Sniper Commando":
Skilldistribution can be something like this:
http://underrail.info.tm/?build=AwGlEYBYQJgVhAdhAZhANhOC01vCgqMVoaQgQnNOgBxgPgwxYwlyZMncPBAMain weapons should be a Spearhead sniper and a Hornet assault riffle, both crafted with the rapid reloader mod (-20% base AP cost) to allow 2 sniper shots or AR bursts per round (2 x 24 AP). Dragunov also works pretty well until you can get a decent qualty Spearhead frame.
Ideally fights will go like this: You snipe from as far as possible the nearest enemy, fire the second sniper round, use Sprint and kite away. Usually the enemies will be too far to reliably hit you and will waste most, if not all AP in order to close in. In the second round, if your chance to hit is good enough, you burst with your AR 2 or 3 times (if Concentrated Fire kicks in) and now that you have your full MP and bonus MP from Sprint you either kite away again (good if you're up against melee opponents) or use Evasive Maneuvers for massive evasion bonus. Base damage output from the Hornet is pretty low so imo it pays off to invest in Expertise, after all you'll be hitting with up to 27 bullets per round. It's not mandatory though so you can replace it with some other feat of your choice. Do make sure to get Thick Skull as it will come really handy late game.
For max damage output you could shed 6 points from constituition and put 2 in perception and 4 in intelligence for Gun Nut but I say that it's a big waste. +15% of upper gun damage is worth something like 10% damage on average. Certainly not worth it to essentially half your max health for that. Gun Nut should've been improved, not nerfed.
I agree with hilf, Aegis is a hell of a drug, especially for a Conditioning build with high constitution and the components are actually not that hard to get with a bit of "farming" in the Foundry mines. As for crafting in general: 3 int is not a problem at all if you use
Junkyard Suprise before crafting. Make sure to buy as many of those as possible. At any point in the game when you need to craft something take a look at the character builder above and put 5 instead of 3 int in to see how your crafting skills will change with the +2 bonus. If your skills exceed the min required numbers you see in the crafting screen, go for it and eat till you get +2 int.
Both weapons I mentioned don't have the best critical hit damage so as an alternate build late game you could focus even more on defense with feats like Nimble, Doctor and Fast Metabolism (Last Stand sucks here because of bad initative). This build is probably a better choice for hard difficulty anyway where healing is very limited: