Rifle Zeros
Rifle zeros are something that is both personal and somewhat misunderstood. The more you understand, the less personal they become. HUH?, you ask?
Experienced 3 gunners, that will shoot at many different matches and therefore ranges will leave the rifle sighted in at the same distance, and learn the differing points of impact at different distances, for the most part. Iron sight shooters may vary their tactic more, simply in order to have the front post out of the way of the target.
Playing with a good ballistic program will give some insight to this. One of the best, and it's also free is JBM Ballistics. It can be found here.
http://www.jbmballistics.com/cgi-bin/jbmtraj_simp-5.1.cgi
Keep in mind that the advent of scopes with graduated reticles can have their own quirks, which are easily worked around. A friend of mine had a Swarvski 1-6X, I'm sorry I don't know the model, just that the retail is past the $2K mark. If you send them your bullet, and velocity, they will tell you about where the range is for each mark on the reticle. ABOUT, you ask?? Yup, atmospheric conditions, temperature, atltitude, humidity, etc, will change how your bullet flies. Luckily, we're not shooting benchrest, but, usually steel plates someplace distant. Anyway, since I use a Burris 1-4X XTR, I'll use this for this example.
Bruce Piatt, someone that is not only a top 3 gun shooter, but, someone that I have known for a good many years, and therefore trust what he writes on the web, stated that since he started shooting a scope over iron sights he zeros his 300 yard dot, at 300 yards with his load of choice. Why not just zero at 100 yards with the center dot/crosshair, you ask? Bruce's zero reduces variation at longer distances, while close targets are not so critical.
Now, if you use a red dot, iron sights, or a simple crosshair for your scope, zeroing at a longer distance and learning where it hits is valuable too. An AR has a sight offset of 2.75 -2.87 inches, depending on the mount. Now, with a 200 yard zero, the highest the bullet will hit, is 1.3 inches at 140 yards, the lowest except at the muzzle is -2.2 inches at 10 yards. If you're shooting close paper in the A/B zone, you simply hold on the top of the target- out to 25-30 yards, then hold center out to 200 yards. What about zeroing closer you ask? You still have the same hold over for close targets, but, as you get a longer shot at 200, you might want to hold high, as the impact the impact will be a couple inches low. The farther zero keeps things simpler.
Now, some folks like to rezero for that close up pistol bay match, which many are. If you shoot Open, with two optics on the gun, one sighted short and the other long makes sense, at least in my simple mind. Keeping consistency will ultimately be quicker over a variety of courses. Your brain recognizes what sight picture will work, and the signal to squeeze the trigger gets sent, time after time.
As in the other threads, I do hope this makes sense to all.