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Ok, this can be complicated, but the short answer is bullet drop and a concept called maximum point-blank range. The idea behind this is that there is about a 12 inch kill zone on a deer, and an 18 to 20 inch kill zone on an elk. An average Whitetail buck is about 18 inches from top of back to bottom of chest. An elk is about 24 inches. The strike of the round needs to be about 3 inches below the spine and 3 inches above the sternum to hit the lungs, heart or major arteries. The width of the kill zone is about the same on each animal, 12 inches and 18 inches, about 2 inches from the brisket back to about the end of the rib cage. A 180 grain bullet zeroed for 200 yards with a MV of 2600fps will reach a maximum of about 2.4 inches above point of aim between 100 and 125 yards down range, and drop 6 inches below line of sight (assuming a 1.5" difference between center of bore and center of crosshairs in the scope) at about 275 yards. With the same bullet, velocity and assuming a .5 BC (Boat tail GK or Nosler Ballistic Tip for example) a 225 yard zero has a max ordinate above line of sight of about 3.1 inches above line of sight, and it drops to 6 inches below line of sight at about 290 yards. It is about 6.9 inches low at 300 yards. Zeroed at 100 yards, the bullet reaches line of sight and begins to drop at 100 yards. At 200 yards, it is about 4.4 inches low, and is 6.5 inches low at 225 yards. This means that you're having to hold over from 200 yards out. With a zero of 200 yards, there isn't a holdover requirement until your target is at least 260 yards away, and with a 225 yard zero, it's closer to 280 or 290 yards before you need to hold over significantly to keep the round inside the vital areas on a deer. Maybe 315 yards on an elk. So the short answer is that it eliminates holdover out to at least 260 yards on deer sized game. A center mass hold will put the round inside the heart lung area from the muzzle out to at least 260 yards, and a hold 2/3 up on the chest will keep the round in that 12 inch kill zone from the muzzle to about 280 yards with either a 200 yard or a 225 yard zero. I ran these figures on the JBM trajectory calculator, assuming a .308 rifle, a 180 grain boat tail bullet, sealevel elevation, and a MV of about 2600fps, which is about what you'd get in a 22 inch barrel. The figures are almost exactly the same for a 165 grain bullet with a BC of 4.2 at a velocity of 2750 fps. So the short answer is it takes a lot of the guess work out of judging holdover and distance. Of course, I could have just said that but I thought you'd like an explanation of why it does.
Me too.
When you had to be a real shooter! Long live the KING!
Long live "long Trang-white feather".
Carlos shot everything from squirrels to big game all day every day. Research how he sighted in and practiced as one of the best snipers in history....
