I am new to the world of red dots and BUIS.  I have always run scopes on my rifles. On  my latest build I am running a Trijicon MRO w/ lower 1/3 cowitnes mount.  I have Bobro Lowrider BUIS.

Its strange now that I think about it but its been years since I have used iron sights.... I think the last time was on an airgun as a kid.  So I am no expert in the use of old fashioned iron sights.

I got the idea of running a range adjustable rear flip up iron sight not only as a backup but  to use for long shots (300-600).  The idea being my red dot would be zeroed at 50m. When shooting at a target at long range I would turn the red dot off and use the irons adjusted for the appropriate range.

I am looking for input on this idea.  As I mentioned I have very limited experience with irons but I know that they are suitable for shots out to 600m as the military uses them at such distances.  

Thanks

The army considers 500M to be the maximum effective range of the M16/M4 for a point target. Keep in mind that as you get to the longer ranges the front sight post is going to cover more of your target. At 300M the FSP is wider than a man sized target. If you plan to do a lot of 300M+ shooting you might be better served with some magnification.

You can get smaller front sight posts, the limit in long range shooting with irons is generally the shooter's eyesight. Have you taken a look at the different combat zeros? Typically, with some practice, a shooter can get pretty used to those and the required holdovers (especially for just ringing steel).

Or you simply start holding high; I've made 1st shot hits out to 500 with an Aimpoint on a IPSC steel.

You just need to understand your round's ballistics. 500 ain't that far.

You should also look up Travis Haley's discussion on Zeroes - I couldn't find the video on a quick search but it's out there.

The post and the dot give you two ways to range a target and two methods to adjust for the shot. Why not? The fixed sights won't be too obnoxious in lower third cowitness, or a KAC 0-600 will fold nicely out of the way.

The magpul MBUS Pro long range is available too

Matech rear BUIS is what the Army issues, OP.  Based on a 300m zero, ranges from 200 to 600 m w/ M855 out of a 14.5" or 20" bbl w/ an F marked front sight.

They do tend to wear out, however.

Just got the latest Primary Arms sale email and they have the Magpul Pro Long Range at a great price if you decide to go that route...

http://www.primaryarms.com/mag527/p/mag527/?utm_source=bronto&utm_medium=email&utm_content=SLOT_10&utm_campaign=16-02-Ad4_Leap_Year&_bta_tid=3.cFU.BzVJBA.Eloj.Asbkag..A4IcqA.b..l.BStr.n...yE0Kxw