Why would you not sight in at 100 yards?

I zero dead at 100 and shoot off MOA reticles or dial if critter is feeding . Have done both , shot 300 yds off reticle in 15 MPH cross wind in Utah last year last year but prefer to dial, it is all the shooters preference where he zeros .
 
Something that has always perplexed me is why guys will sight in their rifles at 150, 200, 300, etc yards. Why would you not just sight in for 100 yards and learn your drops/elevation adjustments for anything beyond that? In my head, if I sight in for 300 yards I need to remember hold-overs for anything past 300 and hold-unders for anything inside 300 which is seems overly complicated. I'm a sight in at 100 yard guy but I want to understand why you would sight in at a different distance as I feel like I am missing something here.
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.
 
My Leupold Rangefinder and scope are best paired together with a 200 yard zero. Both are BDC compensated. I use the varmint reticle from 100 to 600 without touching any vertical adjustment. Beyond that I dial up with a custom turret. They all work great together.
 
I even use mil-dots as holdover for my rimfires (22lr & 22 mag). Works great but hard to find a squirrel you've shot over 50yds sometimes in a hardwood bottom.
 
Best I remember Carlos Hathcock, famous sniper in Vietnam if someone didn't know, used a 700yd zero for his Winchester 70 in 30-06. Guess anything under 700yds just aim at their privates. No mil-dots back then. Just a talented country boy from Arkansas.
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With magnums, 2.5-3" high at 100yds will usually be zeroed at 300yds. No need to "hold under" if shots are 200yds are less. Kill zone on a deer is a lot larger than 3".
 
Think Carlos started hunting with a single-shot 22 rifle. And maybe a one-eyed dog. Think that's a country song. I also started with a single-shot bolt-action 22. It was my Grandad's Winchester model 67. With a single-shot you make every shot count.
 
Whatever works for you is fine...200 for me and then be sure to shoot/practice in the field uphill, downhill, which will throw all this into some new variables. Shoot shoot and shoot again under all conditions you may face in the field. Then you will be ready for most anything...it will be second nature to you, but practice is key to proficient shooting especially LONG RANGE where you can easily wound an animal and ruin your trip and future memories....
 
My cousin and I practice shooting from our deer stands at different distances. We put a target at 300yds, 400, 500, and 600yds. We take turns shooting one shot at each target as fast as we can. Works good for our hunting conditions. I prefer mil-dots for holdover he uses a leupold Boone & Crocket holdover reticle.
 
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