To get this achievement, you have to do all the feats for 1 loadout weapon. To see these for each weapon, you check Track Record, then Feats of Prowess, and then Weapons.
Whichever weapon you choose to do, then you are going to have to get 1000 kills and 500 head shots with it, so choose one you want to use for a while. The exceptions are the Motivator, the Deep Freezer, the shotguns, or the explosives weapons,
Most weapons feats are related to their weapon mods (getting kills with extended mags, killing armored enemies with Penetrator Ammo, ect.). Whatever weapon you choose to complete all feats with, you have to unlock all the weapon mods for that weapon.
I got this achievement with the Bear-Stalker bow since it only has one weapon mod for a feat, but if you don't like that weapon, another easy options would be one of the shotguns because they do not have head shot feats, but instead have close range kill feats. The Deep Freezer freeze gun doesn't have a head shot feat either, but you will have to knife a ton of frozen enemies, so I wouldn't recommend it. The Motivator is another easy choice, but I would only recommend it if you really like being the medic, cause you will be healing for a while before you finish all it's feats. I also do not recommend using any explosives weapon for this achievement, cause good luck getting hundreds of multi-kills with them.
Also, knife kills do not count towards this achievement.