[u]With [b][i]IBSZ[/i][/b] the rear sight remains in the bottomed out position all the time, it is never moved in normal shooting.[/u]
The only reason to adjust the wheel (and go thru the Allen screw drill) is to preserve the utility of the range markings. That is, on the rare chance you see targets at, say, 600 meters, you can click up to 6 and make them wonder where the bullets came from.
In the bottomed out position the rifle is battlesighted from point blank to 220 meters without any adjustments in aiming point. Point and shoot.
There are "click" differences between the 8/3 and 6/3 wheels. On USGI weapons the 6/3 wheels on detachable handles are in "half clicks" and the rear sight needs to be set to 6/3 -4 clicks. The 8/3 sights on fixed handles, including the early M4 Carbine, are in "full clicks."
How to tell? Count the clicks between x/3 and 4. Should be 3 full or 6 half clicks. Set your rear sight appropriately.
Resetting the rear sight is not a requirement of this battlesight zero, only a requirement if you want the range wheel numbers to be meaningful. If you don't care you can skip the Allen screw drill. But it takes maybe 30 seconds after you find the right Allen.
I know of at least four (4) different upper wheels for this rifle system: 8/3, 6/3, Numbered, and Blank. They all interchange, so it's possible to have an 8/3 wheel on a "half click" rear sight -- hence the importance of counting the clicks to determine what rear sight you have.
If you really mess up the Allen screw drill just remove the entire sight, catching the ball detents, and assemble the two wheels on the desk and replace.
-- Chuck