0002S, my objective with an overwatch MBR was to have a scope that could reach out well past 600 yards, conceding that the FAL is not designed as a long range sniper weapon in terms of inherent accuracy AND that I am not that good a shooter yet. But I wanted something with variable power to do the close up work OR a fixed power scope with see through rings to accommodate iron sights. These were the options in my head but I am for sure open to suggestions on alternate options that would allow me to hit targets from afar as well as within 100 yards if need be (where, let's face it, most of the shooting is done).
I routinely shoot at 565, 600, 800, and 1000 yards with a variety of calibers, rifles, optics and iron sights. Here are some real world things to consider past "what scope".
147 grain M80 gets real squirrelly after 800 yards and is not consistently accurate enough to hit a a 1'x2' square at 1000 yards. It will 'do it', just not consistently enough to warrant giving away your position. M80 is great out to 600 yards.
175 M118 ammo is better suited for 800-1000 yard shooting. The issue with the 7.62x51 is that it will go subsonic at around 900 yards and that will effect accuracy at that distance. Another issue is how will it function in your specific semi auto STG.
Your largest limiting factor in distance shooting (past caliber choice) is knowing the exact distance you're target is at. To be effective you will need to know your ranges, angles as well as the dope for you ammo/rifle choice. Then you will need to know how to get that info quickly translated to your optics adjustments. The best rifle and shooters will miss by large margins if they do not have this data and or know how to use it.
Your rifle/caliber choice is your second largest limiting factor to shooting past 600 yards. Your milspec rigger pull WILL effect your accuracy.
Your third limiting factor is going to be your scope mount itself. If your mount is not sturdy enough for repeatability and or causes a check weld that is not easily repeatable you are going to get frustrated real quick past 600 yards.
Also, unless you have a 20MOA mount you'll have issues getting the scope to zero on the cross hairs at 1000 yards with the 7.62x51 round.
Finally your scope choice "can" be limiting past 600 yards. Cheap glass will not have the definition, clarity and contrast to easily focus the target past 600 yards and will be greatly effected by mirage. The mirage with cheap glass can be so bad at 1000 yards as to make it damn near impossible to focus on the actual target. Not to mention it will give you a headache. Again, it "can" be used. I just would choose cheap glass unless i had too. (assuming you have enough come ups in ypu scope/mount to get zeroed at 1000 yards)
Since the purpose of your post is to suggest a scope choice based on your objectives I would suggest that you get a medium to high quality 1-4x and get real good at 600 - 800 yards which is the real world effective range of your rifle/caliber choice. I would also make sure you get a range finder that is good to 1000 yards on semi reflective surfaces. Then I would practice (a lot) at 600 - 800 yards under a variety of atmospheric conditions and if you can a slow moving targets.