Instruction: Output yes if the supporting document can answer the given question. Otherwise, output no.

Input:
Question: Will it work with a 20 inch barrel with an A2 front sight?
Document: The first thing to note is the elevation presets (200-600yd) will only work for military rifles/ammo, so it only works for 5.56mm NATO fired from what I am assuming is a 14.5 inch barrel since several people mentioned they have seen this BUIS on M4s. If you are firing any other type of ammo or barrel length (including .223, because .223 is NOT the same is 5.56 NATO), then the presets will not work.
this sights are excellent for the money, knobs are crisp. just make shure you get the appropriate front sight or you will have to be zeroed at 300y like in my case. it should work fine with fixed front sights.
I first used this sight when I instructed active duty soldiers in rifle marksmanship as part of their pre-deployment work up. Any of the men using red dots had to pull them off after 300 yards and go to their Back Up Iron Sights (BUIS). Once zeroed at 25 meters (white dash between 300 and 400) this rear sight will work for a rifleman out to 600 yards. When the sight is flipped down it's well protected and has a very low profile.
easy to use and straight forward setup. Put it on my AR as a backup open sight. Took the kids out shooting and they loved shooting at 25yds with it. my 12yr old had no issues hitting a 4 inch hanging target over and over again. definitely a great addition to any AR.
This pop up rear sight is a must have for anyone with an AR that has the standard front sight on it. Its one of the few items I've used made for the military that exceeded my expectations. Follow the mounting and zeroing instructions and you will have zero problems.I was very please with the speed I received it. I ordered it late one Friday night and received it in the mail on Monday
Best value I have found. The BDC is perfect, Larue mount +acog clears it just fine, and if I use an Aimpoint or eotech in front of the sight it co-witnesses just fine. Mounts solid and stays down when in the down position.You *must* know your rifle and ammo to get the most out of the BDC... it is a measurement tool. You must know how to use it. There are some good tutorials on the web, please look them up.
This is exactly what I needed to finish out an AR build. It is the same rear sight I used during my deployment to the sand box. Extremely useful for quick range adjustments. It's sturdy, compact, dummy proof, and is a great addition to my holographic sight. For the money I would recommend this sight to anyone looking to add back ups or dedicated sights to your firearm.You may consider buying a front sight tool as well.
Made for close quart and midrange target acqisition and delivers.AR 15 standard issue front sightCal. .223 - 55 grainZero at 27 meters set on 300, adjusted to three shot 1" mao 1/2" under bullseye200 yard shot average 3" moaNo 300 yard range to shot on but I am more than pleased with this sight. The narrow profile allows you to see more target area than the Magpul.
Great iron sight, in every aspect....this is the same rear iron sight that is attached to the colt 6920 socom II limited edition model. I used this rear sight with a standard front post sight for a week during a med/long distance shooting course and it performed perfectly. Ranges out to 600m on the sight, machined extremely well, and the rear post will not accidentally pop up unless some force is applied. Great sight, and would recommend it over any rear sight.
However, due to its length, I can't even mount it to the slot furthest back from the barrel; otherwise, the windage knob interferes with my hand when reaching for the charging handle.
Answer: yes