I have been looking for an adjustable aperture rear sight for my RRA's NM LAR-15.
I have the A2 version fixed sight handle with the .040" peep sight. Brownell's offers this model,

http://www.brownells.com/.aspx/pid=26743/Product/AR_15_M16_ADJUSTABLE_APERTURE_SIGHT

and that brings me to a couple questions:
1) Does this model fit on my RRA's NM rifle?
2) Would this be the model you would order?
3) Is it difficult to install?
Finally,(sorry)
4) Is it legal for 'service rifle competition?
thank you, tom

I don't think this sight would be legal for NRA service rifle.

It's designed to fit on an A2 upper, it would be legal for Match rifle but not Service rifle. It's not hard to change if you have the right size pin punch.

Thanx, Russ

thanks guys.