Practical Ballistics
(300 Yard Zero)

Lacey Washington, October 1999.

My last article for the Goosepit involved how I evaluate my rifle and ammunition for performance.  It is a technique that is about fool proof in terms of sterile range accuracy.  To this point in the Pit, I have been leading you towards a goal of hunting big game.  In this article on Practical Ballistics we will take a look at some reality concerning exterior ballistics and how you can use this information in your sport.  To me, a 300 yard zero is the most mechanically efficient zero one can get out of a modern high power rifle and we will take a look at this.  Sorry, but I have to put out a few more technical terms.  Even if you don’t want to use a 300 yard zero, these terms are part of the education process.

Minute of Angle:  Most hunters use optics and optics have as a minimum, elevation and windage adjustments on them.  Normally the better optics have a ‘focus’ or parallax adjustment but I will not get into this feature.  The elevation and windage knobs have indexes and numbers on them that are graduated in Minutes of Angle or MOA.   A minute of angle is 1/60 of one degree of arc.  This is a very small angle to say the least, but not in terms of a rifle.  You can consider a MOA to equal one inch for every hundred yards of distance.  Thus, one minute equals about one inch at 100 yards, 2 inches at 200 yards, 6 inches at 600 yards and so on.  Two minutes equals two inches at 100 yards, four inches at 200, six inches at 300 and so on.   If you shoot a group at 200 yards that is say six inches below your point of aim and two inches to the left, and you knew your cross hairs were dead center for every shot – you have a mechanical problem that is solved by adjusting your optic.  You will adjust your elevation up three minutes and right one minute and if your gear is working as it was designed, your bullets should center up.  This sounds simple and it is – as long as you know what your optic is calibrated for in terms of increments of minutes.  Take a good look at the elevation and windage drums of your scope.  You will normally see successive numbers going from ‘1’ to ‘X’ with a large index line for each number.  Between this line are probably three smaller lines so you have four each ¼ minute increments between the large numbers.  Your scope is ‘quarter minute’.  Check your windage as well to see how it is subdivided in MOA.  At times, scope manufacturers will use different increments of the minute of angle for the windage than the elevation.  It is common to talk about accuracy of the system of rifle / optic / and ammunition in terms of minutes of angle.   Again this is situational in terms of range but it is better than more graphic descriptions.  Thus a ‘one minute’ rifle is one that you know through real evaluation will hold one inch at 100 yards, two inches at 200 yards and so on. 

Kill Zone:  The game you are hunting has numerous kill zones (Kz).  Knowing the locations and sizes of these kill zones gives any hunter a distinct edge and shows responsible thinking as the hunter then has a good idea of the potential he has for making a humane kill given the different angles he may be faced with in relation to the game while hunting.  The largest Kz’s are normally in a flank shot in the shoulder / chest area.  Due to the size of this area combined with the vital organs and major structural bones located there, a shot in this area gives a good chance of anchoring the animal as a minimum although the animal may not die instantly.  Smaller Kz’s such as the spinal column are extremely small with the resultant chance of a wound instead of a kill.  It is up to the judgment and ethics of the hunter to decide which area he will attempt.  The point to be made is the obvious.  A larger Kz gives a higher probability of a kill without tracking or risking losing the animal.  For most big game, the size of this Kz is about twelve inches in diameter.

Trajectory:  The trajectory consists of a rising branch, the apex, and a falling branch.  The apex is called the ordinate.  The apex or ordinate is a little past mid range.   It should also be known that the rising branch is rather steep with the bullet staying close to its ordinate for about 70 percent of the range and the falling branch is steep to the target.  Bullets don’t float – they drop at the rate of gravity.  The barrel is pointed up when the shot is fired and – given the correct elevation of the barrel – the trajectory is sufficient for the bullet to fight gravity until the bullet strikes the target. 

Pointblank Zero:  This term means that with one zero (elevation setting) and one hold on the Kz, the path of your bullet will remain within the Kz you have determined for your game.  This is normally based on a center hold, so given a twelve-inch diameter Kz; you have six inches above this center point and six inches below it before you are out of your Pointblank Zero range. The military uses the term Danger Space and it is different than a strict Pointblank Zero as for longer shots, the trajectory of the bullet may remain in the Kz from the barrel to ‘X’ yards then rise above the Kz.  Farther down range, the bullet again drops into the Kz and proceeds until it drops below the target.   Thus, Danger Space can be between two different ranges along the path of the bullet while PBZ is only from the barrel to ‘X’ yards.  

300 Yard Elevation:  Now for a little secret.  Damn near every rifle that fires an elongated bullet at velocities exceeding 2500 feet per second will follow along a very similar trajectory to 300 yards.  Take a 25-06 firing a 117 grain bullet at 3000 fps and a 30-06 firing a 180 grain bullet at 2700 fps.  Zero both dead on at 300 yards against a target twelve inches in diameter.  The ordinate of both rounds is reached at about 150 yards.  At 150 yards, the 117 grain 25-06 bullet is five inches above your line of sight, and the 180 grain 30-06 is six inches.  Both rounds fall below the bottom of this twelve inch Kz at about 350 yards.  The question in exterior ballistics is this – does one give you a practical advantage over the other in terms of point blank zero?  The answer in practical terms is no.  A 4000 fps 22-250 behaves the same way as a 2600 fps .308 to about 300 yards.  Go past 300 and you begin to see differences in trajectory and this is extremely evident when one goes past 500 yards.  However – the major differences in trajectory are mostly due to bullet design and weight as opposed to velocity.  That is for another time though.  For the ranges most people hunt big game in the US -- 300 yards or less -- all bullets do about the same thing in terms of trajectory. 

Given this is a simple fact of exterior ballistics – why limit yourself with a 100 yard zero?  Zeroing at 100 yards does not efficiently use the dynamics of the bullet in flight and more importantly, makes you have to estimate all ranges past 100 yards then try to figure out a hold over.  You maximize the efficiency of your ammunition with a 300 yard zero.  All the shooter needs to determine is if the animal is about 300 yards and use a center of Kz hold.   If one is nervous about using this technique I recommend pacing off about 325 yards and putting a target with a 12 inch circle on it every fifty yards with one at about 325 yards.  Use a center hold on each target and you determine if it works.  Note that at 150 yards the bullets will be right at the top of the circle and at 325 they will be right at the bottom but I bet they will be within this 12 inch Kz. 

Commercial Ammunition:  Question you have – given a hundred yard range to zero on, how much above your point of aim should your bullet holes be to equate to a 300 elevation?  Take a look at the back of the box of hunting ammo you have.  Almost all commercial hunting ammo has a little trajectory chart on the back of the box.  What is frustrating about these is that they normally give bullet drop in inches instead of elevation adjustments in minutes of angle.  Take a look at this little chart on the back of the ammo box.  Zero your rifle at 100 yards then see how many inches of drop between 100 and 200 yards; then 200 and 300 yards.  Normally the bullet drop is about 4 inches from 100 to 200 and about 10 more inches from 200 to 300.  Total drop from 100 to 300 is 14 inches.  Fourteen inches equals 4 ¾ MOA at 300 yards.  Add 4 ¾ MOA of elevation to your 100 yard zero and you are as good as you can get for a center shot at 300 without actually zeroing at 300.  By the way – 4 ¾ MOA equals 4 ¾ inches at 100 yards so if your group is 4 ¾ inches above your point of aim at 100 yards – you are shooting a 300 yard zero. 

I hope this little discussion has provided some food for thought with the end state being food for the table this year.  I wish you an excellent hunting season.

 Gene Econ