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Rifle I Magazine

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Wlif le Y Magazine

’Only Accurate Rifles Are Interesting‘ - Col. Townsend Whelen

Volume 1, Number 5 September-October 1969

In This Issue Dodd Registration Bill . . . . . . . . . . . . Neal Knox 10

Pedersen’s Device(s) . . . . . . . . . Maj. George Nonte 16

. . . . . . . . . . . . Departments 1000 Yard Rifles Jim Carm’chel 20

It’s A Royal Custom . . . . . . . . . . . . . . . Staff 23

Fullcircle . . . . . . . . . . Maj. Gen. Richard O’Keefe 24 . . . . . . . Sleeved Actions . . . . . . . . . . . . . . Jim Gilmore 26 Muzzle Flashes . . . . 8

Considering A Conversion? . . . . . . . . . Roy Dunlap 30 Dear Editor . . . . . 12 M1 Conversions . . . . . . . . . . . . . .R. C. Schuetz 32

Bullet Structure . . . . . . . . . . . . . . . Bob HageI 34 LoadingforBear . . 14

ProductProofing . . 64 Rangefinder Reticles: Do They Work? . . . . Ron Terrell 38

Professional Approach to Stocksanding HenryL. Woltman 42 Just Jim . - - . . - 66 ”

Energy & Momentum In Perspective . . . . .O. W. Schoen 46 cover ‘Ballistic Shock’ Formula . . . . . . . . . HomerPowley 51 F;;:; ~~~;;;,i.n‘i;~~~ ;:::

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Change of address: Please give o n e month’s not ice. Send both old a n d n e w address, plus ma i l i ng label if possible, to C i r c u l a t i o n Dept. , T h e R I F L E Magazine, R t . 4--BOX 3482 (1406 H e n d r y x Place), Peoria, I l l i n o i s 61614.

4

The Staff Dave wolfe, Publisher --

Jim Carmichel, Associate Editor

John Wootters, Associate Editor

R. T. Wolfe, Ph.D., Associate Editor

Parker 0. Ackley, Wildcats

John Buhmiller, African Rifles

Harvey Donaldson, Historical

Roy Dunlap, Gunsmithing

Edward C. Ezell, Ph.D., Technology

Jim Gilmore, Bench Shooting

Bob Hagel, Hunting

Neal Knox, Editor

Norm Lammers, Tech. Adviser

Maj. George C. Nonte, Military

Ken Waters, General Assignment

Edward M. Yard, Ballistics

Don Zutz, General Assignment

Rod Guthrie, Staff Artist

John T. Amber, Ed. Consultant

Judith MacDonald, Ed. Assistant

Barbara Killough, Ad. Director

June Skillestad, Circulation Manager

The RIFLE Magazine

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o O T H E R A R T I C L E in The f l Rifi’s short existence has caused so much comment and controversy as Albert0 Perez de Castro’s discussion of “Potence” in the first issue-proving once again how deep the feelings run in t h e heavy bullet, low velocity-light bullet, high velocity argument. Briefly, Perez argued that although foot pounds of energy is the standard comparison of r e l a t i v e car t r idge performance, “experience” has shown that energy alone is not the deciding factor in measuring performance. He pointed out that a light bullet such as the 150-grain load in the .30-06 can be driven at a high enough velocity to give greater kinetic energy than a 220-grain bullet in the same gun, yet experienced hunters select heavy bullets for heavy game. There is far from universal agreement upon this point, but I think that if we were called upon to stop a charging grizzly at point-blank range, most of us would certainly prefer to be armed with a .30-30 and 170-grain bullet rather t h a n a .220 Swif t with 48-grain bullet-although muzzle energy is almost iden tical.

Perez argued that (1) most of us don’t really understand kinetic energy in the first place, and (2) that the f o r m u l a f o r comput ing kinet ic energy-one-half bullet mass times its velocity squared-results in a figure which over-emphasizes the value of velocity as far as cartridge performance is concerned. In an effort to compute a figure more in agreement with 6 6 experience,” he tried multiplying bullet weight times velocity, which is in essence the formula for momentum. He found that the resulting comparative figures were more in accordance with “experience.”

Perez’ theory isn’t new, it’s avariant of, but gives the same results as, the Taylor Knock-Out Theory, which is more than 30 years old and frequently quoted by Elmer Keith.

Before accepting the Potence article, staffer and engineer Norm Lammers and [ discussed it at some length, for

although the kinetic energy formula doesn’t always agree with “experience,” neither does the momentum formula. Holes in both theories were quickly cited by advocates of the opposite position. If you’ve been with us from the first issue, you’ve seen some of those letters and articles written in rebuttal. These ranged from all-out agreement with either the momentum or kinetic energy formulas to total disdain for both formulas; with some experienced hunters contending that, with any modern cartridge, it made no difference what was used or how fast it was going, but simply where the game was hit; and some said the whole secret was in the bullet and how it performed.

Obviously, all of these viewpoints couldn’t be right. For a long time it has been my personal feeling that the answer lay somewhere between the kinetic energy and momentum formulas, with bullet construction necessarily taken into consideration. Frankly, I didn’t .think that it would bec possible to compute all of these v&ables in any kind of formula. I published the Perez article because I believe too much emphasis has been placed upon exclusive use of the energy figures in the ba@tic tables, and I thought the article would stir a healthy controversy-not controversy for its own sake, but a discussion that might lead to new knowledge.

A f t e r no th ing more than an interesting discussion resulted, 1 decided that the article in Rifle No. 3 would close the door on the subject, until s o m e t h i n g new and significant developed. But suddenly there were two developments, the first an interesting letter from eminent ballistician Homer S. Powley, the second a challenging manuscript from a Navy Department physicist, 0. W. Schoen. The Powley letter, published in this issue, details a formula that amounts to a mathematical compromise between kinetic energy and momentum, with the result being termed B a h t i c Shock. Mr. Powley states that he is not a proponent of this formula, but he sent it to us thinking

‘ The RIFLE Magazine < I - - ,

that it might be of interest to you readers.

The Schoen manuscript consisted primarily of esoteric equations and calculations, but the ideas presented were radical and-to me, at least--totally new. I asked Mr. Schoen if he could rewrite the manuscript, putting it “in English.” He did so, ribbing me a bit about the editorial in Rifle No. 1, which said that this magazine would have “a smattering of graduate school courses.” Schoen’s article is still a “gun graduate school” type of article, but you don’t have to be a mathematician-fortunate- ly-to understand his ideas.

Schoen contends that neither kinetic energy nor momentum should be used exclusively in ra t ing comparative effectiveness of cartridges, but that both should be used simultaneously, and that bullet form and construction must be considered. And he has done what few thought could be done-applied all of these variables to a single formula. I t may be that someone can refute his thesis, but it would have to be another physicist-which lets me out. Study his article, give it some thought, and I think you will agree that he has come up with something new and useful-and much

m o r e logical than using e i ther momentum or kinetic energy tables alone.

* * * Mike Keesee was in town the other

day to show us prototypes of the handsome Sharps Arms Company single-shot rifles, which are due to go irto production at Salt Lake City this fall. The company plans to produce the rifles in everything from .17 on up to .50 caliber, with price tags ranging from around the $300 mark.

The rifles are of falling block design, q u i t e s i m i l a r t o t h e original Sharps-Borchardt system, but will be made with modern manufacturing methods, with the receivers to be investment cast - which is the way almost everything new is being made. Extraction of the rimless case is neatly handled, with the block camming the extractor to the right and forward as it is elevated by the finger lever. Although it is only an extractor, it is quite efficient, and when the lever is snapped smartly downward, the extractor wiU pitch a case completely clear of the action.

Trigger pull on the sample rifles was excellent, and lock time seemed very

fast and short, but remember these were hand-built prototypes. P. 0. Ackley wiU be watching qua l i ty control on production rifles, so they may be just as good.

Mike had two guns with him, a .22-250 and a .375 H&H, so George Nonte, Bob Steindler and I took them to the range for some shooting. The .22-250 had a freshly installed lightweight barrel that didn’t match the fore-end and it refused to shoot as it should, but the 375 made up for it. My first four shots went into less than an inch, but the fifth opened up the group to 1 7/16ths - near varmint accuracy, and with 300-grain Winchester factory ammo.

Bill Ruger proved there is a lot of interest in single-shot rifles when he introduced the No. 1 a few years ago - he’s been selling them as quickly as he can make them ever since. I t will be interesting to see if the Sharps meets as warm a welcome - but judging from the reaction at the NSGA and NRA shows, and from my little bit of shooting with the guns, I wouldn’t be a bit surprised. -- Neal Knox. D

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September-October 1969 9

G A T ARTICLE by Albeoo Perez Jde Castto in the fitst issue of The

R i f i was a provocative one, and Norm Lammers summed up the big question in his comments, viz. - “Is momentum a better tool for judging the relative performance of bullets than is kinetic energy?” I n essence, Mr. Perez’ viewpoint revolves around the concept that the mass of a bullet multiplied by i t s velocity is a more meaningful method of comparing bullet potential than is energy. What he referred to as “potence” is in reality an intuitive description of momentum, as Norm Lammers points out. The other often prevailing viewpoint holds t h a t matching the energy of a heavier bullet by boosting the velocity of a lighter bullet will give equivalent results. And here is where the fur starts to fly!

What makes it real fun though is when misconceptions of the rules of nature are presented as physical facts. Not enough can be said for the intuitive approach, but everyone who publishes an opinion should be prepared to undergo an exposure to discussion to help zero in on the propet solution.

Right off the bat I’d like to nail down a couple of those misconceptions a a prelude to a better understanding of the ideas to be developed in this article:

(1) Mr. Perez, in his article, outlined the mistake almost everyone makes in assuming that bullet kinetic energy is conserved within the game animal (tatget). This is usually expressed by

equating the value for kinetic energy from the ballistic tables to the target weight times the distance the target is (mistakenly) moved. Such is not the case, for the following reason: When a bullet collides with a target inelastically, that is, it neither bounces from nor passes through the target; kinetic energy is no t conserved; total energy is conserved (momentum is conserved also, but that doesn’t concern us here). Quoting from the article, “An engineer wants to know that an object striking with 2,000 fp of kinetic energy will move a 1,000 pound second object a distance of two feet.” Fortunately for the game animal this is not the case! As the reader may verify by reviewing the design features for a ballistic pendulum, the ratio of final kinetic energy (KE2) to initial kinetic energy (KE1) is given by Equation I

KE!2/KE1 = m/(m+M)

where m is bullet mass and M is target mass. Since the target mass we are taking about is so much greater than bullet mass it is completely safe to say that the h a l target kinetic energy (ICE?) is negligible. AS a bullet is about to impinge upon a target its total energy

for al l practical purposes consists of its initial kinetic energy (=I). After the bullet has come to rest within the target i t s t o t a l energy (TE) consists of Equation 2: TE = KE2 + Heat Energy + Sound Energy + Mechanical Energy. The energy lost through conversion to heat and sound is quite small. The final kinetic energy (KE2), as we have seen, is also small and in reality moves a large game animal just a few thousandths of an inch. The mechanical energy consists of the work required to cause plastic deformation of the target and to raise internal pressures through a volume change. Most of the initial kinetic energy is converted to this form of work and is usefd to the hunter.

c.

(2) In the third issue of The Rifle, in another article concerning energy and m o m e n t u m , t h e e x a q q l e of a momentum of 100 ft-lb/sec as an invariant with respect to effect on the s h o o t e r i s i n c o r r e c t . Because momentum is numerically equal t a impulse (mv = Ft), recoil effect at any valug for momentum can be reduced by %crea&g the time during which the recoil force takes place. Increasing the time has the effect of reducing the peak forces involved. I refer the reader to the recent application of a spring-loaded device imbedded within a stock that takes advantage of this concept.

Now down to business. In this article I will point out what factors are involved in the selection of proper bullet weight and velocity for optimum field use, and how bullet expansion fits into the picture. Some of the arithmetic can get a little involved, but for the most part 1 think the explanations are fairly complete. I know of no other way to develop the concept that follows.

For convenience, the table used by Mr. Perez has been rearranged for consistent units and is included here as Table 1 to allow the reader t o more

The RIFLE Magazine

conveniently set up his own examples. The example I use is for the case of two .30-06 bullets, 150-grain and 220-grain, compared at equal energies and also at equal momenta with properties as listed in Table 2. In these tables, and in all the work that follows, energy is expressed in units of ft-lb (mass), momentum in ft-lb (mass)/sec, and mass in Ib (mass). The key to using proper and consistent units is that a pound of mass is the familiar pound of force, or weight, divided by the gravitational constant “g” (32.2 ftlseclsec), or lbm = lbf + 32.2 ft/sec2. This step must be made in all calculations so that all units are consistent, otherwise the answers will be wrong. I t doesn’t make any difference whether you always use pounds mass (lbm) or pounds force (lbf), but since bullet energy is always listed in ballistic tables using pounds mass I’ve presented all units in this way.

If we assume that the useful part of the bullet energy that is delivered to the target (Mechanical Energy) is of m a x i m u m use when t h e bul le t penetrates completely without exiting from the far side, then this is the fmt clue in finding out what is needed to derive an expression telling us what it is that bullet penetration depends upon. As a first step in working out this expression, or equation, the bullets must be considered to be constructed so that expansion within the target is the same for both, otherwise a meaningful comparison cannot be made. Once the calculations are done then we can see what a change in expansion causes. Also, external dimensions and shape of both bullets must be the same, which is easily controlled by considering the 150-grain bullet to have less lead at the base and the void filled with less-densc copper.

As the bullet moves through thc target its motion is opposed by a retarding force which results from the September-October 1969

viscosity of the medium and depends on the shape of the bullet. For the sake of comparison it’s necessary to assume both bullets meet the same resistance within the target. This resistance can be called “resistance factor R” and when this R is multiplied by the bullet velocity within the target, the result is the force tending to stop the bullet. This expression is found in most physics books and is written as Equation 3:

F = -Rv

The negative sign is necessary because if R were increased, by making the bullet fatter for example, then the velocity v within the target would go down. In studying the meaning of the terms in this equation note that the negative force on the bullet at any time t depends only on R and v, and that this negative (decelerating) force goes up if either the bullet velocity or the target resistance is increased.

Now is the time to tie in the weight

of the bullet with this equation. Also, since we know that distance D + time t is equal to velocity v, with a little fiddling around maybe something useful will come out. First, we can replace the bul le t retarding force F with its equivalent expression for decelerated bullet weight. This expression also is found in most physics books and is written as Equation 4:

F = (W/g)a which is a shorthand way of saying that any force F on an object is given by, or equal to, the mass of the object (weigbt + gravity) multiplied by its acceleration. In this case the retarding force F is negative and the acceleration is really a deceleration (negative acceleration), so: t he minus signs cancel out. Since retarding force F is equal to both of these expressions, as s t a t ed by Equations 3 and 4, then Equation 5:

by subs t i tu t ion . Now all of the (W/g)a -Rv, or ma = -Rv

47

necessary ingredients are there and all that’s left is the job of working them around to find out what we want to find, which is OK as long as no physical or mathematical rules are fractured in the process.

T h e f i r s t s t ep is t o change deceleration a to velocity v + time t, or more correctly the change in velocity (VZ-VI) divided by the change in time (tz-tl) is equal to the deceleration:

Then grouping like quantities together, Equation 6:

(v2-~1)/v = -(R/m) (tz-tl)

Slipping into calculus for awhile in order to integrate this thing, and then taking the anti-logarithm of the result gives us Equation 7:

v = vg e-(R/m)t

where v is the bullet velocity at any

given time t, vg is the bullet velocity as it enters the target (we’ll use muzzle velocity as a convenience), m is bullet mass, and R is the bullet retarding factor which depends on bullet external characteristics, as noted earlier. The “e” is a number (2.718) resulting from that last calculus operation and is raised to t h e power given by the exponent -( R/m) t.

-

The second step is to find the bullet penetration D resulting from its velocity v and the time t it takes to come to a stop.. But it’s not just a matter of multiplying v times t unless the velocity is a constant value. If it’s not constant, as in this case where it’s slowing down to a stop, then we’ve got t o lean on calculus one more time and integrate again, which is just a special way of multiplying. This results in an answer we can use - an equation telling us what factors control penetration depth - Equation 8:

D = (mvg/R) ( l-e-(R/m)t)

From this we can see how bullet p e n e t r a t i o n depends o n bul le t momentum, where mvo is the bullet momentum as it is about to enter the target. Nowhere in this equation is there an energy term and regardless of how long it takes the bullet t o penetrate, the deepest it can ever go is given by D (max) = mvg /R.

This means then that maximum The RIFLE Magazine

penetration can be increased either by decreasing the resistance factor R (reducing bullet expansion) or by increasing m o m e n t u m . I f energy happens to be increased while the h a n d l o a d e r is busily increasing momentum, as is bound to happen, so much the better as long as it’s safe, but energy is not a controlling factor for penetration.

In order to see a little more clearly why this is so, let’s graph this equation for both the equal energy case and the equal momentum case as described in Table 2. We need a value for the retarding factor R in order to solve for penetration distance D at any given time t, so let’s assume that the 220-grain bullet at a momentum of 2.4 ft-lbm/sec penetrates to a maximum of 2.0 ft. This indicates the bullet doesn’t expand very much and drives right on in, but it’s OK for an example. It can be left as an exercise for the reader to duplicate the following work by using 1.0 ft. as a max. penetration distance for this bullet. Substituting these values for mvo and D into Equation 8, where the quantity in parentheses equals zero when time t is long enough for the bullet to reach D (max), Equation 9:

R = mvo/D = 2.4/2.0 = 1.2 lbm/sec.

This value for R will be the same for b o t h b u l l e t s s i n c e t h e y ’ r e (hypothetically) constructed for equal expansion characteristics.

The curves in Graph 1 show that two bullets of equal energy travel pretty much together within a target, but that t h e bul le t of higher momentum penetrates deeper. This will always be the case when two externally identical bullets with equal energies meet the same target resistance; the higher momentum bullet will penetrate br ther and expend i ts available energy throughout a greater portion of the target.

Of course if too high a momentum is used the bullet will exit the far side of the target, which does no one any good. Note the effect of bullet expansion in this case. Increased expansion will result in an increase in retarding factor R, which lowers the penetration curve in the same way as would decreasing the momentum. That is, maximum bullet pene t ra t ion depth is reduced as effectively by decreasing the bullet momentum mvo as it is by increasing the R factor via increased expansion. The big difference though is that bullet September-October 1969

energy is not reduced when expansion is increased as it is when momentum is decreased. So when a target calls for less penetration without a reduction in delivered energy, R should be increased by choosing a more rapidly expanding bullet. This is perfectly logical and is a vote of confidence for Equation 8.

Curve 2 in Graph 1 shows that if a 220-grain bullet at a momentum of 2.4 lbm-sec and an energy of 2,930 ft-lbm penetrates to a depth of 2.0 feet, then in comparison a 150-grain bullet at the same energy, where the corresponding momentum is only 2.0 lbm-sec, penetrates to 1.67 feet. The curves

49

would remain unchanged if curve 2 represented the 220-grain b d e t under the listed conditions of energy and momentum, and curve 1 represented the same 220-grain bullet, still at the listed conditions, except with the retarding factor R increased from 1.2 lbmlsec to 1.8 lbmlsec by increasing the expansion. This is usually what happens when a load designed to expand properly on a lighter game animal, such as deer, is used on a larger and heavier animal, such as elk; the bullet expands within the larger animal before proper penetration is attained, with the result that energy is not properly dissipated within the target. The usual remedy when going to larger game, due to the increased effective target density and greater penetration required to reach vital areas, is to reduce the rate of bullet expansion so that final expansion occurs deeper.

The curves in Graph 2 show that two bullets of equal momentum penetrate the same distance and that the higher energy (lighter) bullet attains maximum penetration depth sooner. But note in Table 2 the energy and velocity required in this par t icular example! The mathematics say that this load will do a better job compared to the 220-grain since more energy is expended through the same distance, but I doubt if there are very many who will operate their .30-06 a t t h e required pressures. Besides, when velocities approach about 4,000 fps and higher, all bets are off and we have to derive new equations. More about this later, but right now let me emphasize that juicing up a light bullet to equal a heavier one in energy is not enough.

This results i n a comparison represented by Graph 1 and the light bu l l e t j u s t doesn’t compare i n penetration. Boosting the velocity of a light bullet high enough to equal a heavier one in momentum, in order t o get the penetration, is generally grossly inefficient and most likely dangerous. This results in a comparison represented by Graph 2. This is not to say there aren’t exceptions. There might be a published load somewhere with such a low momentum that a jazzed up lighter

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version of the bullet will exceed not only the energy but also the momentum (penetrat ion) characteristic without getting into dangerous pressures, but I can’t think of one. 1 think it’s safe to say that as a general rule you have to work with momentum to drive the bullet in where you want it, and energy to get a quick and clean kill. All energy at the surface is no good, and all momentum out the far side isn’t much better.

As an aid in using all this information several curves have been drawn up to eliminate the need for plugging values into equations and solving. Graph 3 is drawn from the equation D (max) = mvo/R with curves for various target entrance velocities; Graph 4 is drawn from the relationship between bullet energy and momentum, also with curves for various target entrance velocities; Graph 5 is drawn from the momentum equa t ion , with curves for various momentum values. For convenience, the bullet mass in Graph 5 is also shown in grains weight so as to eliminate the need to multiply bullet mass by a constant t o get the more usable figure.

The first step in selecting a bullet to perform a required job in the field is (1) to determine the bullet velocity at the target, the velocity you want or are forced to accept by circumstances. The Speer calculator is handy for this sort of thing, or the more general “Exterior Ballistic Charts” published by E. I. Du P o n t de Nemours & Co., Inc., WiLmington, Del. Next, (2) decide what penetration you want, depending on the target size, and read off the bullet mass to bullet resistance ratio m/R from Graph 3. (3) From Graph 4 choose the energy you want t o deliver to the target and read off the momentum required to deliver this energy by using the proper velocity curve. (4) Enter Graph 5 at the bullet velocity at the target, go to the curve for the momentum as found in Graph 4 (interpolate if necessary), and read across to the bullet mass. This completes the process except for one step: R is assumed equal to 1.2 lbm/sec as per the assumptions leading t o Equation 9. A proper value is needed

we’ll have to wait for the manufacturers to come up with the tables, or else do our own experimenting.

As an example, suppose it is desired to penetrate a target to a depth of eight inches and the bullet velocity at the target is 2,000 fps. Using these values in Graph 3 the ratio m/R = .00033 is found. Next, suppose a bullet energy of 2,000 ft-lbm is required at the target. Going to Graph 4 and using the 2,000 fps velocity curve again, a momentum of 2.0 ft-lbmlsec will be necessary. Now, using this value of momentum at 2,000 fps velocity, the required bullet mass of .OO1 lbm, which is equivalent to a weight of 225 grains, is read from Graph 5. The bul le t expansion characteristic R is found by dividing the bullet mass by the bullet m/R ratio, i.e., .001 + .00033 = 3.0 lbmlsec. This is the value for which, unfortunately, there are no published figures-yet.

But this doesn’t mean we can’t use these ideas right now. All one has to do to find a good value for R for any one bullet type and caliber is to record field data of penetration distance and bullet momentum for each shot (for one type of target, such as deer or elk class) and substitute the average values of several shots or so into Equation 9. When R is - found this way, new values of bullet momentum can be calculated using mvo = RD for any new penetration distance desired. . *

As mentioned earlier, when bullet velocities get up to around 4,000 fps and higher this approach will no longer woyk. This takes us into the realm of the ultra-high velocity bullets and their unusual effect on a target, so that the energy-momentum combination really is not the question. It’s an interesting problem a n d I’m sure someone eventually will come up with a description.

Summing up, then, 1 think it has been pretty conclusively shown that the energy tables by themselves do not give the hunter enough information to make a wise choice in picking bullet weight and velocitv to fit exoected field - - , -

for R in order to realize optimum penetration, and then since the value of m/R is known (Graph 3) and the value of m is known (Graph 5), R can be

conditions. i u g h g moLentum and expansion together to get the right penetration is one requirement; the other is to use as much energy as I found. All that is left is to choose a Dossible.

bullet with expansion characteristics t o fit this value of R. Unfortunately, I don’t think bullet testing has ever been done with this in mind and I’m afraid

50 D

The RIFLE Magazine