C'mon guys - try the following search string:
http://www.google.com/search?sourcei...or+Iron+Sights
It gives you access to a lot of relevant info. In fact it'll connect you to the answers for most of the current questions.
NDD - FWIW I've seen a different 25M Zero target for the M4. It was not the same as the M16A2 target. The squares are not the same size and the aim point is different. You can use (everybody does mostly because they don't know any better) the M16A2 target; it doesn't make any difference except for the clicks to adjust and the POI (elevation - not critical at <150M especially with M68s/Eotechs). I've been looking for an M4 .pdf but haven't found one yet. The manual I've been able to access doesn't have the targets. I'll keep looking. Peregrino