Re: .308 BUIS?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: _9H</div><div class="ubbcode-body">The AMU, other .mil teams (All Guard for example) and some civies are running the CMP/NRA legal Servie Rifle for long range (800-900-1k) in this site configuration:
http://www.762sass.com/product.php?p=366&cid=9&session=1cde35bb6912e55c6b225677b251d3ae
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BIG +1 on this suggestion.
Your average BUIS (regardless of whether they are 5.56/223/7.62/308/etc.-specific) aren't designed to be precision instruments for accurate, extended range fire. They do "okay" but are FAR from ideal and not something that I'd generally want to trust for getting the job done at long range. Generally BUIS get slapped on a rifle and then never fooled with. If people do take time to adjust them and get them zeroed for a specific range...adjustments are coarse, difficult to adjust in any hurry (or non-adjustable) and thus, make for a terrible solution if you need to go from a battle-zero to accurately putting rounds on target at extended ranges. Also, some BUIS suffer from return-to-zero/repeatability issues because of the "flip-up"/retractable design.
On the other hand, the AR-10 NM carry handles that _9H suggested are great inasmuch as they have national match, hooded rear sights with 1/4MOA windage and elevation adjustments and a NM front sight post. Having used them (and with the limitations irons have from teh get-go), I can tell you that I'd be willing to bet on placing rounds accurately and consistently on target at 600yds+. However, as with other BUIS options...you still have issues with the return-to-zero, repeatability of the sights as they mount up with standard thumb-screws. Getting them removed and reinstalled with similar torque, etc. is crucial to repeatability and I don't know how well they achieve that end.
Here is the BUIS "braintrust"...see if you see anything you like:
http://www.ar15.com/forums/topic.html?b=3&f=18&t=206233
Also, FWIW and if you have the means...here is LL's proof-of-concept for arguably the best "back up" you can get for any AR-platform rifle/carbine:
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