I had ordered and now received a Colt detachable carry handle for my RRA LEGP. What I never seen before is that the elevation knob has 6/3 instead of the usual 8/3. Should all adjustments in zeroing be made the same as if I was zeroing at 100yards as if it was the 8/3 elevation knob?

ArmaLiter

Yes, the zeroing is the same. I once read what the difference was (20" to 14.5" barrel?) but I can't remember now.

Elevation clicks on the M16A2 are one minute per click.  Elevation clicks on the M4,or any other piece using the detachable handle, are 1/2 minute.  Therefor, when you come all the way around on the M4 wheel, you've only raised the sight enough for 600 meters.  The wheel will turn past that point, and you might get enough extra elevation out of it to get close to 700 meters, but I'd rather have the 1/2 minute adjustment and forget about anything further than 600 meters, especially w/the shorter barrelled M4. If you want to check it out you'll find that it's 6 clicks from 3 to 4 on your M4 handle, and only 3 clicks on your A2 sight. Hope thi helps

Whoops, kind of forgot to answer you original qestion about sighting in.  Yes. if you're using SS109 or ballistically equivalent ammo, and you zero at 300 meters, the higher numbers will put you on at 4,5,&600 meters.  Now, my Bushmaster detachable top will go ten clicks (5MOA) beyond that.  The elevation reading on my fixed top AR shows that the elevation change from 6 to 7 is 6MOA, so even at max elevation you're not going to quite get to the 700 meter level.