Battle Sight Zero – a somewhat technical discussion

“Battle Sight Zero” is a phrase used by the U. S. Armed Forces (and probably others) in two separate but related meanings.

* First meaning is the concept of combining the properties of the trajectory of the bullet (which depends on the firearm – usually rifle and the loading of the round used), the effectiveness of the bullet loading (that is, how far it will either dispatch or seriously wound an enemy soldier), the effectiveness of the bullet in maintaining a true flight (accuracy in terms of wind drift), the size of the target (in this case the torso area of a ‘standard size’ adult human belligerent) and the line of sight of the rifle and shooter in such a way as to maximize the probably of a hit for the furthest possible distance. When determining this condition, ‘elevation’ is the only sighting variable considered. One is on one’s own for windage.

Depending on the authority and the round in question this elevation is a distance of up to 20 inches. This is NOT a single point targeting technique. The rifle is sighted – aimed – at the belt or waist level of the belligerent up to a specified range, then, again depending on the rifle and ammunition, aim may be shifted to shoulder level.

* Second meaning is the actual sight setting for an individual and rifle (and load) which causes the proper combination to achieve the above. For instance, for the U. S. M14 rifle with ball ammunition, the sight setting is the 300 yard rapid fire setting, MINUS two clicks [lowered elevation]. Other rifle and ammunition combinations will vary.

Trajectory diagram 30-06 2

The above illustration (NOT TO SCALE) is a diagram of trajectory and battle sight – danger zone – setting for the M14 rifle with ball ammunition (M59). This is remarkably similar to the U. S. military .30(-06) M2 ammunition fired from a rifle. They are roughly the same bullet weight and type at the same muzzle velocity. (Not perfectly identical.)

The blue line indicates the trajectory of the fired bullet. Note the bullet is above the line of sight out to 400 yards range. The highest or greatest change from line of sight is called the ‘mid-range trajectory” – which is not really at the mid point of the trajectory, but early on shooters thought it was. (This ignores the first 25 yards or so of flight where the bullet is lower than the line of sight. However this distance can never be more than the distance between the muzzle and the sights – typically a matter of one and one-half inches; perhaps a bit more with a telescopic sight. This ‘lower than line of sight’ area is insignificant, unless one is firing at a fly or spider.)

From the muzzle to 400 yards, the bullet from the rifle under discussion will impact a human torso presumed the rifle is correctly aimed at belt level. The blue rectangles represent the torso area of a belligerent. The entire range where a specific bullet will strike a human torso (with either belt line or shoulder hold) is the ‘Danger Zone’.

Notice the blue rectangle past the 400 yard Second Intersection. The ‘Battle Sight Zero’ distance can be lengthened by – at a certain distance depending on the trajectory of the rifle/cartridge used – aiming at shoulder level. The bullet is still falling, but by aiming at the shoulder level the bullet will still impact the target area for some distance.

As noted, the illustration is NOT to scale. However, since a falling object (in this case, the bullet) falls faster with time (which corresponds to downrange distance in this case) the first portion of the ‘danger zone’ is longer than the second portion of the ‘danger zone’ past the Second Intersection.

This technique can also be used in hunting. The target zone (either heart/lung or spine/neck) is smaller, therefore the ‘danger zone’ where the trajectory of the bullet not rising over X inches from line of aim is shorter. One notes the small the target area, the shorter the danger zone or effective range for this technique.

The technique does NOT work well for formalized target shooting, where the 10 or X ring is smaller still.

How far is the danger zone? This depends on the cartridge and load used. From the illustration, one should note a ‘flatter’ trajectory makes a longer danger zone. Conversely, a ‘higher’ trajectory makes a shorter danger zone. It should be apparent the danger zone begins at the muzzle; clearly the bullet cannot depart from the line of sight/aim sufficiently to miss a torso sized target between the muzzle and First Intersection with the aiming line.

A second limitation for the ‘danger zone’ is the effectiveness of the bullet at range. At some range, all ammunition runs out of power – usually determined by kinetic energy – and will no longer deliver a suitable blow for the purpose at hand. At whatever range a hit with a given round will not injure the belligerent, seeking hits at that or further range is pointless.

So how does one – the average shooter – use this technique and knowledge to one’s advantage. Glad you asked.

Ground rules. This will work with any rifle and any ammunition – to different results. A .30 Winchester Center Fire will not have as much range as a .300 Winchester Magnum, typically. However, one can get the maximum range from the rifle and ammunition combination as is possible. The shooter must be able to shoot a ‘group’ from the rifle in question. That is, with the shooter’s selected ammunition, the shooter must be able to deliver at most a five inch grouping at 100 yards. In other words, if one cannot shoot worth a hoot, this probably won’t help.

Step One: Determine the rifle and ammunition to be used. In many cases, this will be the rifle one has. Then decide which brand and type of ammunition that best serves one’s needs for the use intended. Some may choose a quasi-military rifle and the ‘regular’ ammunition which is intended for such rifle. Or one may buy an exotic rifle and hand load for it. No matter – pick A rifle and A type of ammunition.

Step Two: Determine the trajectory of the selected rifle and ammunition. No need to make a graph, like I did, but simply have a table showing the drop of the bullet (from the selected ammunition). Some of the loading manuals have this and I’m sure the information is on line some where. One may also look up the ballistic coefficient of the bullet used, actual velocity and calculate it – but I’m not that compulsive.

Step Three: Determine the allowed target size for intended use. The vitals of a deer are bigger than the width of a prairie dog. Both are considerably smaller than the torso area of a marauding, predatory human evil-doer.

This ‘allowed target size’ determines just how much elevation from line of sight is to be allowed. For instance, a six inch diameter ‘target’ limits the mid-range elevation of the trajectory to six inches.

Step Four: Determine the maximum effective range of the rifle/ammunition selection for the purpose intended. Pretty much any hit one can make on a prairie dog will be effective, regardless of caliber or loading. A deer or moose will require some greater level of kinetic energy to kill humanely. Any rifle/ammunition selection will – at some range – lose energy down to an unsatisfactory level. Such distance may be shorter than the range at which one can score a hit on the intended target. This rather limits the ‘battle sight zero’ range.

Step Five: Fit the information from Step Two into the allowed parameters of Step Three. Make sure the elevation at the ‘mid range’ point is NOT outside the parameters of the intended target.

Step Six: After determining where the ‘battle sight zero’ should register at 100 yards (note in the diagram above, the 100 yard difference in bullet impact is 8.6″), go to the range.

First, shoot at 25 yards to ensure a zero setting. With most modern calibers, this will put one on paper at 100 yards.

Then, shoot at 100 yards to match the 100 yard impact from the range and drop table. Remember the ground rule about ‘shooting a group’? One may well ask “How am I supposed to have the group be 8.6″ high?” The answer is to have a ‘group’ more or less centered 8.6″ above the aiming point. Do NOT aim 8.6″ high, aim at the bull or aiming point and adjust the sights so that the bullet impacts are – on average – 8.6″ above the bull.

There are other problems at times. A rifle equipped with buckhorn or otherwise ‘open’ sights utilizing a ‘wedge elevator’ may be difficult to adjust perfectly.

Historically, the Springfield 1903 rifle first used the 1903 cartridge. Then in 1906 the Army decided to change rounds and started issuing the 1906 (.30-06) round.

The two rounds are nearly identical, except the ’06 round is slightly longer. The serious difference is the ’03 round used a 220 grain bullet at a muzzle velocity (officially) of 2300 fps; the .30-06 used a 150 grain bullet (with a slightly better streamlined shape) at a muzzle velocity of 2700 fps. This difference in bullet weight and velocity alters the trajectory noticeably. The ’06 bullet simply shoots flatter.

It is more complicated, of course. In 1926, the Army developed the .30 M1 Ball to better accomplish indirect fire in machine guns. This round was somewhat heavier and slower, but had better long range ballistics in terms of retained velocity. Then, 1938 the Army found the M1 round would shoot too far for some ranges, and the M2 round (more or less the original ’06 round) was developed. All of which have different trajectories.

This is further complicated by current ‘claims’ by the U. S. Government. Army Technical Manual TM 43-0001-27 published April 1994 is titled Army Ammunition Data Sheets Small Caliber Ammunition FDC 1305. Small Caliber includes up to .50 BMG rounds.

Page 5-9 lists information for “Cartridge, Caliber .30, Ball, M2” the .30-06 Springfield round mentioned earlier, in common speech. The TM has NO listing of the bullet weight (traditionally accepted as 150 grains), but lists the propellant as “IMR 4895, 50 gr”. The chamber pressure is listed at “50,000 psi” and velocity as “2740 fps, 78 ft from muzzle”.

One notes this information (combination of bullet weight, powder charge and velocity) is somewhat verified by reloading information.

Speer loading manual #14 shows 150 grain FMJ BT with a maximum of 49.5 grains of IMR 4895 for a velocity (chronograph distance not provided) of 2722 fps.

Hodgdon #26 shows 150 grain bullet (not further defined) with 49 grains of IMR 4895 at 2852 fps (no details).

Lyman #49 shows a 150 grain jacketed soft point bullet with 51.5 grains IMR 4895 at 2958 fps and pressure of 49,200 C. (Fired from a 24 inch Universal receiver.)

Hornady 9th edition shows loadings for .30-06 Springfield and a separate section for M1 Garand. Neither section lists loads for a 150 grain bullet with IMR 4895 powder.

The 7.62 (x 51) NATO round (very much the same as the .308 Winchester) for the M14 rifle seemed to maintain essentially the same loading for ball (infantry) rounds. (Page 11-3 of the TM, if anyone cares to look.)

The last few statements are merely to reinforce the idea that even the Army sometimes ‘over advertises’ their figures.

The M16, et al then reintroduced the problem. Not satisfied with the original M16, the various Armed Forces decided to change the physical shape of the arm, usually shortening the barrel (called the M4, if memory serves); which changed (lowered) the velocity of the issue round. Somewhere in this process, the issue round was altered to fire a boat tailed bullet, which caused a change in retained velocity. In other words, a different trajectory.

One also notices the 5.56mm NATO round lags to just over 400 foot-pounds of kinetic energy at 400 yards. This is enough for a fatal wound IF in a suitable location, but may not inflict a serious non-fatal injury at such range. One also notes the wind drift suffered by the rather light bullet fired by the 5.56mm round at ranges greater than 300 or so yards.

For these and perhaps other reasons, the 5.56mm NATO round usually has a battle sight zero determined ‘danger zone’ of not more than 300 yards. On the other hand, the 5.56mm round battle sight zero setting normally has bullet strikes no more than 8 inches or so above line of sight. Additionally, the 5.56mm round seems to not use the ‘shoulder hold’ concept. On the one hand, it somewhat limits the ‘danger zone’ of the battle sight zero. On the other hand, I never could remember the exact range to switch from belt to shoulder and I was never good at range estimation.

One can determine the ‘switch’ range. When the bullet impact ‘falls’ with range to the point of aim, one then moves the point of aim to the top of the target area. One will have to do some range testing to find this point, or calculate it from drop tables. Using the information for the arm being used, of course.

That’s it. Actually, it’s simpler than it looks if one remembers the bullet trajectory is a curved line in space (technically called a parabola) and it always, always, always happens.

Since I began writing this, I’ve found a ‘cheat’. The web site http://www.jbmballistics.com/ballistics/calculators/calculators.shtml
has a calculating program where one can enter the details for one’s own rifle or pistol and get a full result. One might have to ‘play’ with it a bit. Ballistic coefficients are not available for obsolete and proposed rounds, but it will do.

However, what I’ve outlined here is the basis of the calculations in the web site.

Just for the tally-book, I am not associated with that web site or any products or services sold therein. (Other than lip, sass and grief, no one gives me much of anything; other than my retirement and God, who simply loves me more than I deserve.)

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Filed under Firearms and their use, physics

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