Tactical Skills for an Adventurous Life

An Effectiveness Study of the Infantry Rifle

We’re going to continue our look at historical documents that led to the development of the M-16. As before, we’re setting the way-back machine to the early 1950s and the dawn of the atomic age. Once again, I want to acknowledge the work of historian Daniel Watters, whose 5.56 timeline lives over at Loose Rounds.

In 1948, the Army stood up the Operational Research Office (ORO) to investigate new warfighting methods in the era of nuclear weapons. By 1950, the ORO’s research expanded into conventional small arms.

The Army’s Chief of Small Arms Research and Development, Colonel René R. Studler, looked at the ORO’s expansion as a breach of his territory. Col Studler, like many other combat veterans of the era, stood firmly in the camp of full-power rifle cartridges like 30-06. To head off the ORO, he commissions Aberdeen’s Ballistic Research Lab (BRL) to begin its own study of infantry rifles.

Donald L. Hall heads the program starting in November of 1950.

Previous Work

As with any study, the first step is usually a review of the literature.

For this, Hall went back into the archives and dug up the work of Robert H. Kent. This study, if you recall, mathematically showed that a smaller projectile fired at higher velocity would be better at transferring ballistic energy to a soft target. Additionally, these smaller caliber bullets offered flatter trajectories and the ability to carry more ammunition per soldier than the heavier .30 cal ammunition.

As part of this study, Hall wanted to set a standard for the weight of rifle and ammunition. He settled on a standard weight of 15 lbs, derived from the weight of the M-1 and 96 rounds of M-2 ball ammunition. This was the recommended load provided by Colonel S.L.A. Marshall in his popular book, The Soldier’s Load and the Mobility of a Nation. When it comes to individual load carriage, Marshall is pretty much the thought leader of the era.

Hall also cites the work of Dr. T.E. Sterne, who published a study in 1951 for the BRL about the probability of explosive fragments incapacitating a soldier. The study, ironically identified as Technical Note 556, is officially titled Provisional Criteria for Rapid Incapacitation by Fragments.

Performing the Study

Halls study really took place in two parts. The first part, like Kent’s before it, was theoretical. The second part was practical.

For the theoretical work, the study focuses on the probability of a single shot to incapacitate a target. This probability falls into one of three categories, defined by Dr. Sterne:

  • “K” type incapacitates in five seconds or less
  • “A” type incapacitates in five minutes or less
  • “B” type is severe wounding that might be fatal at some point

For the purposes of the study, Hall discounted any effects of gyroscopic instability that induced tumbling or fragmentation. Since the lighter bullet was more likely to do this than the heavier, but the consistency wasn’t predictable, they left it out. So keep that in mind, these findings are excluding the potentially devastating effects of fragmentation.

Theoretical Findings

The trick of the study was multiplying the expected probability of hitting the target against the probability of causing a severe wound. Hall made several curves detailing different calibers and charge weights.

The charts did not transfer well, but I’ll talk you through them.

This first chart details the relative hit probability of a .21, .24, .27, and .30 caliber cartridge at different charge weights. The range, in yards, spans the bottom. The takeaway here is that a lighter bullet with faster velocity has dramatically higher probability of hit than the baseline .30 cal M-2 ball cartridge.

That mirrors the predictions of Kent’s study in 1930.

The next chart plots the relative wounding power of each bullet. It uses the same bullet calibers and charge weights.

The plot stops before the curves start to drop off precipitously, but you get the point. Hall combined these statistics with data on how much rifle and ammunition could be carried for the 15 lb limit and made the following conclusion

Summary

In general, it can be stated that if the combined weight of rifle and ammunition is fixed at 15 lbs, a man carrying the Cal .21 rifle would have an expectation of killing about 2-1/2 times as many targets as with the M-1 rifle. The range at which this occurs depends on the amount of charge. The 0.6 charge rifle is most effective at the short ranges because of the lighter ammunition. The 1.0 charge is most effective at the longer ranges because of its flatter trajectory.

The final curves of the relative overall expected number of kills show that rifles with heavy charges are preferable at the longer ranges, but those with the lighter charges are made preferable at the short ranges. It is beyond the scope of the present report to state which is the optimum rifle, for this would depend on the most probably combat range…it might be concluded that a rifle that is more effective at ranges up to 500 yards should be favored over one that is more effective at ranges greater than 500 yards.

That last paragraph ultimately came to fruition the following year with Norman Hitchman’s study.

Practical Testing

Well, you can imagine that these results flew in the face of Colonel Studler. Roy Weatherby’s .220 swift cartridge, which fired a 48 grain soft-nose bullet. Everyone knew that the .220 swift was inadequate for hunting, so how could it possibly beat the mighty 30-06?

Hall convinced Studler to provide a custom Winchester rifle with a 1/10 twist and 200 rounds of ammunition. This ammunition used a 60 grain .22 bullet shaped like the well known .30 Carbine bullet.

With only a limited amount of ammunition, Hall tests the accuracy and ballistic characteristics. To simulate tissue, he fires reduced power loads into clay to measure the cavity.

To assist with these efforts, Hall gets the help of Aberdeen’s William C. Davis, Jr. and Gerald A. Gustafson. That may seem like a small fact, but these gentlemen have a huge impact later, so to speak.

This is from the conclusion:

This was a rather small sample of experimental data, and it is doubtful if any firm conclusions can be drawn from it. However, if it could be assumed that a bullet will behave in flesh the same way as it did in the modeling clay…it could be concluded that for the same striking velocity, the Cal .22 is practically as effective as the Cal .30. This may be due to the fact that the Cal. .22 appeared to tumble in the clay at all the velocities considered. Furthermore, under the above assumptions, since the Cal. .22 will have a higher striking velocity than the Cal. .30, the severity of the wound for a given range should be much greater for the Cal. .22 than for the Ca. .30.

Put another way, the tumbling effect of the .22 at closer velocities made it just as effective, if not slightly more so, than the tested .30 caliber M2 ball.

Ammunition

In the notes, Hall talks about the shape and performance of the ammunition.

The statement that a 7.0 cal ogive would provide better ballistic characteristics and range was interesting. I did some digging, and it turns out the 77gr SMK has a 7.0 cal ogive.

Things that make you go, “Hmmmm….”

Now, before you go away thinking that this study clearly venerates the 5.56 and proves that Jeff Cooper’s “Poodle Shooter” statement was wrong, just hold on. Hall listed the ballistic data about the test cartridges. The 60-grain bullet sat atop 40.5 grains of IMR 6363 and had a screaming muzzle velocity of 3660 feet per second.

That is far faster than modern 5.56 loads, but it does show you what velocity can do.

Conclusion

Like other reports, Hall concludes his study by listing the things he was unable to determine and should be studied.

The theoretical consideration of a family of rifles indicates that smaller caliber rifles than the .30 have a greater single shot kill probability than the Cal. .30 M-1. This is obtained by increasing the muzzle velocity and thereby obtaining a flatter trajectory, so that the adverse effect of range estimation errors is reduced.

This ties together Kent’s 1930 report and predictions. The summary continues on with recommendations:

A smaller caliber, higher velocity rifle than the Standard Cal. .30 is more effective than the Cal. .30 when compared on the single-shot basis; the basis of equal combined weight of rifle and ammunition; the basis of load required for equal amount of ammunition carried; and on the basis of load required for an equal number of targets killed.

It is recommended that tests be conducted to determine the following information:

(a) Single-shot hit probability as a function of range, missile velocity, and obstacles such as brush or vegetation

(b) Probability of causing certain types or rates of incapacitation as a function of striking velocity and projectile weight.

(c) Effect of recoil on the probability of hitting for semi-automatic and automatic rapid fire.

I emphasized points A and C because those are exactly the things Norman Hitchman tested as part of Project BALANCE the following year.

Now…whatever happened to Gerald Gustafson and William Davis, the two men who performed the test firing for the experimental rifle?

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