Why Army and Marines have differnt zero standards?

[flenna]

Well all I know is that my POI is always low when I run my drills anywhere from 5 to 30 yards, not high. I'm zeroed at 100. Still baffled as to Haley's results.

That is due to the height of the sights over the bore- at close range it will shoot noticeably low.

[miyagi]

I always zero with Federal XM193... if I'm going to shoot something else and I'm not being real serious about it, I'll just shoot a few rounds of the other ammunition and see where it impacts. I'f it's close I'll just make a mental note of it, if its drastically different then I'll change the zero making a note (on paper) of what it took to zero so I can walk it back to the XM193 zero. My Nikon has been very consistent at returning to zero.