I bought a Bushy carry handle from a member on this board to go on my new flat top upper. It was in great shape, but the screw that holds the rear sight elevation index together with the elevation adjustment was missing. I got a new screw from BM when my upper came in. I don't really think this screw is for an allen wrench, it looks round on the top instead of polygonal. How do I get this thing tightened down in that hole?

As for sighting in, should I set the elevation half way up from the bottom, zero the rifle using the front sight adjustment and then move the index to 8/3 and stake her down? Please excuse my ignorance.


Sorry the picture is out of focus, but you can see the screw and hole that I'm talking about well enough. Thanks in advance!

http://plaza.ufl.edu/daven/P1010456.JPG

That Elevation Index Screw should take a 1/16" hex Allen Wrench.  If it don't, its not the correct screw, or the hex has been stripped out.
Either way, you would need a "new" correct screw.

When you install the screw, secure it when the elevation dial is about 3 clicks below the 8/3.  When you zero for elevation, make adjustments only to the front sight post.
Because most of us don't plink at 300 meters, those 3 "minus" clicks will put you closer to point of aim = point of impact at 100.
I have found on most uppers that more than -3 clicks on the rear will force you to rotate the front sight post so many clicks counter-clockwise for a 100M zero, that the post will be up so high as to wiggle, or up above the a-frame's protective ears.

Thanks for the info about the allen wrench I'll give it a try. I understand that I should zero with the rear sight 3 clicks below 8/3. However, the index spins independently until the screw is in. What I'm asking is how far up or down should I have the rear sight when I put the screw in and say, "this point right here will be my 8/3"? Halfway?

Rotate the bottom portion of the elevation dial counter-clockwise until the rear sight assy moves all the way down and the dial stops turning.  Now rotate the dial clockwise 3 clicks and fire your first group.  If initially firing at 25 yards or so, your group should be an inch or so below your point of aim. Fire onver sand bags from a solid prone position using a big, clean target.  Make all subsequent range adjustments on the front sight/windage to the rear.
Move back the sand bags back to 100 and refine your front sight post elevation and rear signt windage adjustments by firing a few more groups (3 rounds per group is all you need fire).
If you want a 150 or 200 yard zero, do some more walking, shooting , and adjusting, but you want the rear sight assy "up" about 3 clicks from being all the way down.  Once you have your elevation zero here, you do not move the front sight post anymore.
If you are a very good marksman, you will now have a good "prone supported" zero at whatever range you decided on (100, 150, or 200).  But if you will mostly be firing from lets say a sitting position at 100, you then need to practice that by shooting 5 or 10 round groups, as you may need to add or remove a click or two to compensate for your eye position changing as you assume difference positions.  A click or two of elevation in these cases should be made at the rear sight--that's the second purpose of the extra 3 clicks "below the 8/3".