I have a Oly AR with a 16 inch barrel that I got a couple of months ago.  I finally got it to the range this week and tried to sight it in at about 80-85 yards.
 I got it on paper but I'm afraid that if I raise the front sight enough to get my usual 2-21/2 inch high at 100 yards zero, the front sight is going to unscrew completly.
 Do I need a taller front sight  or can I just keep on unscrewing this one?  It shot great groups(aprox 2in. which with my eyes and iron sights is great).  
I know that this is not the "proper" sighting procedure, but I prefer all my centerfire rifles sighted this way, and I'm comfortable with it.  
Thanks
Frank

Suggest you check out the Santose method here:
communities.msn.com/TheMarylandAR15ShootersSite/zeroingmethods.msnw

For your rifle the Santose 50 yard method using M193 or M855 will keep your POI within 1.5" out to 300 yards. This is a very popular zeroing method here and one which I employ w/ my personal CQB AR.

Mike

Thanks very much for the info, that's what I'll do.
Frank  

Quoted: Suggest you check out the Santose method here: communities.msn.com/TheMarylandAR15ShootersSite/zeroingmethods.msnw For your rifle the Santose 50 yard method using M193 or M855 will keep your POI within 1.5" out to 300 yards.

Uhh its 2" from 8M to 220M.  At 300 yards you are about 4" low, at 100 yards you are roughly 1.5" high...

Yes it is an excellent zeroing method, its the one I use on my AR-15s and recommend it to almost everyone (the only exception being High-Power match shooters).