Hello all - this is my first post on the board.  I've been lurking for a few days.

I'm in the process of trying to sell my SA XD .40 S&W pistol to fund the build of a tack-driving AR-15.  Since I first saw the Bushmaster Varminter reviewed on Gunblast I was in love with it.  It's way out of my budget, so I'm thinking I'll build my own.  I'll probably outfit it with a Super Sniper because I like the reviews they have gotten, and the price is reasonable.  Plus they don't have that "deer rifle" look.

Anyway, I want to build the rifle first, then get the optics when I can afford it - so I'll probably fit the rifle with the flip-up sights.  My question is this: How accurate will the rifle be once the scope has been removed, and reinstalled?  Does the gun need to be sighted in again?

Also, what kind of MOA difference will I see between the 20 and 24 inch barrels?  I think the 20 looks better, but accuracy is what I'm after.  I'll probably never find this kind of distance, but if I ever wanted to reach out to 500+ yards, I'd like to know the rifle was up to the task.  I've always been interested in target shooting, but never had a gun that was capable of precision shooting.  Will a 20" barrel be any good for those distances?  Will the 24" be?  Or is the AR-15 .223 the wrong gun entirely for those ranges?  I saw a similar question posted a couple of days ago, but it seemed to veer off into the realm of human-sized targets, which is obviously much larger than little varmints.  

I'm not a service guy (lost a leg in a motorcycle wreck back in 96) - I just want something extremely accurate, on a shoestring budget.  Is that possible?

Be gentle...

In response to your question regarding maintaining the accuracy of you sights after they have been removed from the flat top.  I highly recommend investing in a LaRue Tactical sight base.  LaRue products are second to none and they will maintain accuracy even after repeated cycles of mounting and removing your sight from your weapon.

Here is a link: http://stores.homestead.com/Laruetactical/StoreFront.bok

hint: look under "optic mounts"

I took off my Larue cantilever / ML2 so I could  Install my KAC RAS etc.

My zero at 50 yards hasnt change a bit


Im not to worried about it since its a red dot sight


BTW

My A1 20 inch HBAR chrome lined  by Bushmaster shot ragged holes at 100 yards with 69 gr BTHP

I have the LaRue SPR-E mount on my 18 inch SPR style AR15.
I have never had any issues with having to find center once the scope/scope mount has been removed from the rifle.

You'll never regret spending the money on the LaRue.