I can't get logged into AR15.com and they need a not free email account to re-register so I'll throw this out here.  If you can get logged in there maybe post it there and see what you get for answers. I have this Midwest Industries flip up rear site and it sucks.  I dial it in for the close range aperture and when I flip to the long range one it's four inches high, which it should be, but it's also five inches right, which it should not. 

Have you ever checked yours?

Anyway I want to ask on there what is a good tried and true proven rear sight.

I can't get on AR15.com either. Have you tried a site search over there?

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Best is more of an opinion.

I think Magpul MBUS-Pro and Troy brand are very good but also very expensive. I do not own a set, so I cannot give you my personal experience with them.

https://www.magpul.com/firearms-accessories/sights/see-all

https://troyind.com/backup-iron-sights


I have several sets of the plastic Magpul MBUS sights. They work OK, but I doubt they would ever win any national matches. Right now PSA is offering a set of Black MBUS sights for $49 with free shipping. You will not find it cheaper. Use code "MBUSSET" in the coupon window when checking out. If you see them on eBay, they might not be the real gun sights. Magpul also has a cheapo set for airsoft guns that frequently shows up on eBay.

http://palmettostatearmory.com/magpul-gen-2-mbus-front-rear-back-up-sight-set.html



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https://www.magpul.com/products/mbus-pro-lr-adjustable-sight-rear




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I run the standard Magpul BUIS rear sight on a couple of guns.  They aren't precision sights, but if you miss a soda can at 100 yards it's your fault and not the sights.  And they are quite reasonable.

http://www.letmegooglethat.com/?q=best+AR+flip-up+rear+sight


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https://www.ar15.com/forums/AR-15/The-big-bad-BUIS-FAQ-Page-1-updated-on-8-4-2006-/18-206233/

Thanks for the replies.  I bought a Midwest Industries (rear is crap), a MagPul, a Mag Tech, GG&G and a set from Griffin Armament.  Hands down the best rear is the MagTech.  Maintains it's windage zero from 200 to 600 yards.  Has one aperture and just raises and lowers it.  Any one who has shot across the course will appreciate the aperture and the elevation adjustments.  Second place would got to the GG&G.  It blocks out a lot of the side view but the site is dead on from aperture to aperture.  Requires a little concentration to lower it where the Mag Tech is just grab it and flip it up, flip it down.

Knight KAC 600m Rear Sight large knob

Knight KAC M4 Folding Front Sight