bore sight-in on 200 yards

[pashok23]

Thanks Bob 

[LEN]

Thought I was remembering my physics. This is right from the book on a falling object. Point being you start at 0 and at 1 sec you dropping at 32 fps so the first second you drop 16 feet.
This o fcourse this assumes your wife isn't the one who pushed you over the edge.

 Time interval   Avg. speed   Dist moved   Cumulative distance
  -------------   ----------   ----------   -------------------
  0 to 1 second    16 ft/sec      16 feet       16 feet
  1 to 2 seconds   48 ft/sec      48 feet       64 feet
  2 to 3 seconds   80 ft/sec      80 feet      144 feet
  3 to 4 seconds  112 ft/sec     112 feet      256 feet


OH and just for the record all my big game rifles are sighted at 200 yards.

LEN

[ICEMAN]

Based on a few comments on  this thread, it appears that some do not understand the path of a bullet fired from a scoped rifle.

Bullets are affected by gravity and pulled downward at 32 feet per second per second from the moment they leave the muzzle of the gun.

The bullet starts below the line of sight. How far below depends on sight height. Most scopes are about 1.5" above the bore. That means the bullet starts 1.5" below where the crosshairs are pointing.

The barrel is angled slightly upward relative to the line of sight, and therefore the bullet is rising relative to where the sights are pointed. With a gun sighted in 2" high at 100 yards, the bullet first passes through the line of sight at around 30 yards. It continues in a relatively upward path, and at 100 yards is 2" high. It continues rising until it reaches its mid-point trajectory. With a 2" high 100 yard impact, a modern centerfire bullet reaches this mid-point height at around 125 to 150 yards. It then begins a relatively downward path, getting closer and closer to the line of sight. It crosses the line of sight at somewhere around 200 to 300 yards, depending on the bullet's velocity and ballistic eoefficient. It then continues to drop relative to the line of sight, getting further and further below where the crosshairs are pointed.

The only way to have a gun be zeroed (hit the point of aim) at both 100 and 200 yards is to have the scope about 5" above the bore. That's not practical.

The scope should be around 1 1/2 inches above the bore. For big game it's usually best to have a modern centerfire shoot a couple inches high at 100 yards. With a 270 firing a 130 grain bullet at around 3100 feet per second, and sighted in 2" high at 100 yards the bullet will have a mid-point trajectory of around 130 yards where it is 2 1/4 inches higher than the line-of-sight. It will be zeroed at around 235 yards. It will be 2" lower than the line of sight at around 260 yards. That makes 260 yards the "Maximum Point Blank Range" and means you can place your crosshairs on the animal from 0 to 260 yards, and the bullet will be within 2 1/4" of where you are aiming, plus or minus shooting error.

The most important thing is to practice shooting, and understand your limitations. Shooting from a bench is a good way to select ammuntion and understand the inherent limitations of your equipment, but is no substitute for field shooting experience. Unless you hunt deer from a bench rest, you must practice shooting offhand, prone, kneeling, and other positions you will use while hunting.

My rule of thumb is 90%: 9 times out of ten my first shot will place the bullet in the vitals of the animal. You can use an 8" paper plate as a good target. The distance at which you can hit the plate 9 times out of 10 shooting offhand is your maximum offhand distance. The same goes for the other positions.

Here's a good article on external ballstics to learn more: http://www.rifleshootermag.com/2010/11/02/shooting_tips_ballistics_0303/

Bob, your write up is without a doubt the absolute best description of this topic I have ever read. Kudos!!!

You should consider copy and pasting into a sticky so it can be revisited by members all year long.

Again, thanks for taking the time for such a well worded, clear write up.