5" at 100 will give you about a 400 YARD ZERO...give or take roughly .6 of an inch. Zero your gun at the distance you want zero...if you don't have access to that distance then a ballistic calculator will tell you based and load and speed. That being said...if you are trying for at 200 yrd zero about 2.4" would be closer
For decades I employed the old 3" high at 100 yards sight-in method. This was the max point-blank range concept, and it revolved around the six-inch circle that somebody once wrote about as being the size of a deer's vitals. The max PBR for most of the cartridges we used was in the neighborhood of 225 to 250 yards, and this was all fine & dandy.
Now, when anyone still uses this sight-in method, the magic number seems to be 2.5" high at 100 ( as cited above ) and I think this came to be around the time we started seeing all the plastic-tipped bullets come on the market. BC's were improving, so the trajectories were flattening a bit. This trend has continued to the point where the whole max PBR concept is falling into dis-use, and more guys are now dialing their scopes for long range shooting. The definition of the term "long-range" has changed pretty dramatically in recent years, as well.
Another thing that has changed this is the increase in the use of range finders among hunters. It used to be that guys would get a "flat-shooting" cartridge, sight in 3" high, and figure out at what range a top-of-the-back hold would still kill the animal. Then they would call that their maximum range. If the animal looked pretty far away, they would try that hold and see what happens - if they shot under, then they figure it was too far.
Things were far simpler then, but but simpler isn't always better. With the bullets we have now, the old concept works better than it has ever worked in the past - but it still doesn' work better than what most guys are doing now.
