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September 14, 2012, 09:02 PM   #16
Scorch
Senior Member

Join Date: February 13, 2006
Location: Washington state
Posts: 12,862
Quote:
 please explain +/- 4" MaximumPoint Blank (MPB) trajectory
When fired, the bullet travels in an arc that crosses the line of sight at about 50 yds, then again farther out, where depends a lot on velocity, zero range, etc. So a lot of people zero their rifles at 100 yds then try to calculate the range to their target and compensate by aiming higher on the animal. This sometimes causes people to miss the animal completely.

The MPB method is simplicity itself: just find out how large the vitals of the animal you are hunting is, then sight your rifle so that as the bullet rises and falls it never goes outside of that dimension out to a distance you can calculate.

A deer's vitals are about 8" across, so you want to find what range you can sight in for that will keep the bullet's path within that area, in this case 8" or +/- 4" from your line of sight. So play around with the JBM software a little, telling it what the velocity is, what the ballistic coefficient is, and what the weight of the bullet is, and adjusting the zero yardage until you can see from the output that the bullet does not rise or fall more than 4" from line of sight (+ will be above line of sight, - will be below line of sight). Then look at where the output says the bullet strikes at 100 yds, and zero that many inches high at 100 and feel relatively confident that you will be able to hold dead on your target and hit within that +/- 4" out to X yards without having to hold over.

If you have questions after you have tried the JBM software, you can PM me.
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