Fun fact my 1911 Swiss rifle is zeroed for 300 meters, and well the sights don't adjust for less than that either. They were trained to shoot for the belt buckle and since most combat is closer its going to hit high. Interesting philosophy. Drove me nuts first time I shot it until I figured it out.
That's exactly what I was talking about in my earlier post, when I suggested using a 6 o'clock hold with your 300m zero at all ranges from point blank to 350. If you always aim for the bottom edge of the target, this will compensate for your trajectory. It works for targets that are both closer and farther away than 300m. It has to do with how many minutes of angle the center of the target is from the bottom edge of the target at various ranges.
USMC James knows what he's talking about... when you are zeroing a rifle for the first time, you always start with the front post even with the FSB and the windage centered. You set your rear elevation drum for the correct setting for the range you're using, and then make your elevation adjustments at the front sight, so your elevation drum will be correct.
I have been told that the Marines are trained not to use the small aperture. They do like USMC James said and install their rear sight drums so that they will go 2 clicks below the 300m setting (which is usually where it bottoms out, from the factory), and just use the small aperture for everything. But FYI, the large aperture is 2 MOA lower than the small one, which is how far the bullet drops from 200 to 300m. It is designed to take you from a 300m zero to a 200m zero. However, 2 MOA is also how far the bullet drops from 100 to 200m, so if you did it the USMC way, and you were 2 MOA below your 300m setting with the small aperture, you ought to have a 100m zero if you flipped to the large aperture.
Now all of this goes for a rifle with standard rifle-length sight radius and a 20" barrel. When you go to the carbine-length sight radius, the clicks on the elevation drum are more than 1 MOA because of the shorter sight radius. However, the lower muzzle velocity of the carbine-length barrels generally makes up for the fact that you're adjusting in larger units, at least for the ranges they are intended for, so the BDC and dual apertures work pretty much the same as they do on the standard length rifles.
It's pretty neat how all this stuff works. These sights were designed by some pretty smart dudes... not as smart as John C. Garand, who designed the sights for the M-1 and M-14, but I digress!
Close enough for jackrabbits, coyotes, deer and prairie dogs.
