How far are you considering ‘long-distance’ in this case?
Because you have to keep in mind that the game does (somewhat poorly) model loss of momentum (and the associated damage fall-off), and it only renders particle effects for registering hits within a certain distance. So, stuff that will be a one-shot kill (or only take 2-3 shots to kill) at 100m can easily take dozens of shots at 500-600m, and you won’t see any visible feedback that anything has hit until you actually kill the machine (or destroy a component, because for some reason the particle effects for that get rendered regardless of distance).
Based on my own experimentation, it’s almost impossible to reliably engage any target more than about 400-500m away with anything other than the Pvg 90 (the Gvg works too if you use it like a howitzer, but the math needed to get it to land accurately is far from easy, especially against moving targets). The Pvg 90 itself actually has insanely good accuracy out to about 800m (tested with the help of a friend who was calling shots for me against a fixed target), which is a bit short for a Barret M88, but is easily accounted for by your character not realistically having any proper training. Damage fall-off seems to be pretty low too, but that makes sense (a .50 BMG round maintains supersonic velocity for quite a while, and it’s the transition from supersonic to subsoinc that really kills damage potential (because it reliably destablizes the bullet)). The Gvg is also pretty consistent and has no damage fall off (which is really realistic), but it takes a lot of practice to use effectively past about 300m because of the arcing trajectory (longest shot I’ve made so far with it was almost 750m, though it was against a group of runners so accuracy didn’t matter as much).
The Älgstudsare and Meusser are good to maybe 400m with a good scope, if you account for bullet rise (yes, bullet rise, not drop, the curves are a bit longer and higher for these guns than they probably should be), which while a bit unrealistically short, is within reason for someone with limited training.
The AG 5 seems to be good to about 250 meters (beyond that accuracy is too poor), which is actually rather realistic (5.56x45mm rounds (and .223 Remmington) really do have poor accuracy beyond about 250-300m, but maintain velocity better than larger rounds due to lower drag). The AG 4 is good to about 150-200m (further than that damage fall-off is just too much), which is a bit short but within reason against a hard target for 7.62x51mm rounds. The AI-76 is only good to about 150m because of accuracy, but that’s pretty realistic (real life AK’s have crap accuracy past about 100-150m unless they’ve been modified for it).
The HP5 is good to maybe 100m in terms of accuracy (if you’re burst firing and not going full-auto), but damage fall off is pretty severe past about 50m, which is kind of backwards (9x19mm Parabellum rounds are good to maybe 70m from most SMG’s, but still carry enough force to punch through light armor without significant difficulty out to maybe 120m). The Kpist shows similar behavior, but with slightly beter accuracy (can’t comment on how realistic that one is, I don’t know enough about the internal ballistics).
For the handguns, you’re lucky if you do much of anything with them past about 25m, and they’re all useless past 50m, which is actually really realistic (though the insane bullet drop of the .44 Magnus is not). If anything, the Möller PP is actually more accurate and has less damage fall of than an actual Walther PP (which is not much use past maybe 10m against a soft target).