I just got a 20" C7 style upper and am looking for tips on how to sight it in.  Most of the procedures I find are for the A2.  I rarely shoot past 200 yds, so I've been thinking of the Santose method...which aperature should I use (the marked or unmarked)?  
I've heard people say to replace the rear sight and use an A2, but that would limit the windage adjustment.  Would it be safe to enlarge the unmarked aperature with a drill to create a larger (low light) aperature?  Does anyone make an A2 rear sight but in the A1 size?
Also, since the A1 aperatures look the same, how does it "really" change the impact when using the short range (unmarked) vs. the long range (marked)?

FWIW the C7 and C8 uppers have the small and larger aperatures like the A2.

I would replace your rear if I were you.

It's dirt simple:

1.  Zero the (L)ong range aperture at 25 meters.  Point of aim equals point of impact.

2.  Flip sight back to short range aperture.  You have a standard 250 meter zero.

Note this is meters, not yards.  27 yards is close enough.

-- Chuck

Here is a link for the online procedure,

[url]http://www.geocities.com/Pipeline/2494/A1Zero.html[/url]