Someone just asked a similar question- if you do a search you should find the post and that had a lot of information - long and short- It's pretty much an obsolete system and you are better off with a Shepherd, USO SN4 with the JP1 reticle or ACOG. If you want to shoot farther than 500meters I would reccomend the huge 5 power ACOG's if you plan on going that route. It just seemed to me that it got tough and dicey to range targets past 500meters with any speed because it's kind of like ranging a thumb tack at 35 yds.
To be fair though I was shooting kneeling and that might have added difficulty, and I know a designated markman with 2 confirmed kills on running terrorists at 820meters. [.308 acog M14 Arms base and throwlever rings and M118LR ammo] (one three shot and one two shot) so apparently it will work at distance I just think it's a tougher system to work with and maybe some people have slightly better vision than me who knows?