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The Original Silver Bullet
Rifle Magazine
September - October 2004
Volume 36, Number 5
ISSN: 0162-3583
Number 215
On the cover...
The prewar Beissel & Winnieckl 9.3x74R is outfitted with a Leupold M8-2.5x compact scope. The Krieghoff O&U 9.3x74R double rifle features engraving by Bob Evans and custom stock by Paul Dressel. The scope is a Leupold Vari-X III 1.5-5x. Rifle photos by Gerald Hudson. Elk photo by Michael H. Francis.
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Analyzing Accuracy

There have been a number of requests asking for the psi and CUP equivalents for several rifle cartridges. The list shown contains the MAXIMUM ALLOWABLE for respective cartridges - NOT THE MAXIMUM AVERAGE.

For most of us, any discussion of rifle or handgun accuracy is summarized in terms of groups - extreme spread - or the measurement between the centers of the most widely spread bullet holes. Most of the time, it is easy enough to just lay a ruler or caliper on the target and measure between the centers of the widest bullet holes. If the group is somewhat clustered, it may be just as easy to measure from the outside edge of the widest bullet holes and subtract the caliber of the bullet. This is the best method and probably the only practical way to measure a group that is little more than a one-caliber hole, albeit generally calipers that are accurate to within .001 inch are required.

That’s how I measured a one-holer that was fired from a stock off-the-shelf Remington Model 700 .30-06 with handloads using the then-new Hornady SST bullet. At first, I was satisfied that it was basically a one-caliber hole, but when measured from the extreme edges of the hole and subtracting .308 inch, the three-shot group actually tallied as .005 inch. I’ve been shooting rifles since 1952, and that is the only one-holer to come my way.

Actually, the idea of measuring groups from the center of the widest bullet holes is relatively new. For many years, the U.S. Army used one of two measuring techniques: mean radius and figure of merit.

Mean radius is sort of involved and requires two lines, one drawn vertically through the bullet hole to the far left, or right, and another through the center of the hole at top or bottom of the group.

Let’s assume I have five bullet holes in the target, so I draw a vertical line through the hole on the extreme left and a horizontal line through the lowest hole. Then I measure from the line on the left to the center of each of the remaining bullet holes. Then I’ll do the same from the horizontal line to the center of the holes, and then average the distances from the vertical and horizontal lines. Let’s say the average shot is .5 inch from the vertical line and .7 inch from the horizontal line. Add .5 to .7 and divide by 2, leaving .6 - the mean radius.

The mean radius is a good method for measuring groups because it tells us a great deal about the spread of the bullet holes around the point of aim. In this example, we have determined that the five shots landed, on average, within .6 inch of where the sights were pointed. Additionally, that means if you aimed at the center of a golf ball at 100 yards, any one shot will hit the ball, albeit within a .6 inch radius of the center, or point of aim.

I’m partial to this method because it explains in easy-to-understand terms that a seemingly marginal 1.5-inch, five-shot group from a sporting rifle actually means you can call the shot within .75 inch from the point of aim based on a worst-case scenario. If most of the shots are clustered within one inch, with one flyer, then the potential is there to put any one bullet within .5 inch or so of where you want it. You can also state that rifle is capable of holding shots within .5 inch of where the sights are pointed, indicating a bit better accuracy than would be implied if accuracy is simply stated as the spread between the center of the widest bullet holes.

Statistically minded readers will also notice that mean radius is roughly the mathematical equivalent of standard deviation and is used to measure the potential accuracy of a given load over several samples, or groups. Either way, mean radius offers a bit more information than group diameter, which has little to do with the field efficiency of sporting rifles.

Figure of merit was also used   by the U.S. Army but was usually restricted to measurement of smaller groups that were somewhat clustered or contained a larger number of shots that pretty much confused accurate measurements.

Figure of merit is simple enough: measure the vertical and horizontal spread of the group, add them together and take the average. So, you can have a 10-shot group that spreads 3.5 inches wide and 5.0 inches tall, for 8.5 inches and a figure of merit of 4.25 inches.

Likewise, you could have a group that spans 7.0 inches vertical and 1.75 inches wide (I actually fired a group like that at 80 yards with a .45 Colt revolver), for a figure of merit of 4.375 inches, a number quite close to the sample above, but somewhat deceiving if both groups were posted together.

No doubt, those who shoot targets will continue to use group   diameter as the standard measurement of accuracy. For hunting, however, where we do not shoot groups in animals, what we really want to know is how well any given rifle will hold its shots to the point of aim or intended point of bullet impact.

* * *

Marlin Wish Lists

I’ve received quite a bit of correspondence over the last few months from folks wondering why Marlin does not chamber a variety of cartridges, including the .454 Casull, .405 Winchester, .45-90 WCF, .50 Alaskan, etc.

So, I’ll try to approach this in a methodical manner. First, overall cartridge length: The Marlin Model 336 (aka Model 95) can handle cartridges up to 2.55 inches in length. That eliminates the .348 Winchester, .35 Winchester, .405 WCF, .45-90 WCF, .50-100, .50-110 and a few other wildcats based on the longer cases.

Yes, the Marlin can be modified to accept longer cartridges, but it’s a painstaking one-of-a-kind job. Moreover, I am not aware of any custom gunsmith who has actually “proofed” a Marlin Model 336 after it has been changed to accommodate longer or larger cartridges, e.g., .50 calibers, and may suggest that the folks at Marlin know something we don’t about their lever actions.

The next problem is pressure. The Marlin Model 336 is limited to approximately 44,000 CUP operating pressure. That leaves out the .358 WCF or any case based on the .308 WCF, like the .243 Winchester. That also eliminates the .500 Smith & Wesson, .454 Casull, .357 Maximum, etc.

This also applies to the Marlin Model 94, which is commonly chambered for the .45 Colt, .357 Magnum, .41 Magnum and .44 Magnum, all of which have a pressure ceiling of around 40,000 psi or less. And again, while it may be possible to modify the action slightly so it will chamber the .357 Maximum, for example, the little Model 94 is not designed to take the factory-rated pressures of over 51,000 CUP.

* * *

If you want all the power and recoil you can stand in a lightweight, easy-carrying lever action, the best option right now is the Winchester Model 94 Traditional or Traditional CW .480 Ruger at 6.25 pounds with a hard rubber (plastic?) buttpad and 20-inch   barrel. Marlin is offering the Model 1895RL .480 Ruger and .475 Linebaugh with an 18.5-inch barrel and pistol-grip stock (nice touch) with ventilated recoil pad and sling swivels at 7 pounds.

And, some might not be aware that Legacy Sports International chambers its little Model 92 (Winchester Model 92 copy) for the .454 Casull - with a very thick buttpad. Even if you don’t load the little carbine to maximum pressures, it should offer about 250 to 300 fps more velocity in the 20-inch barrel than might be generated by the same load in a revolver.

Lastly, while it’s off the subject just a bit, a number of folks have wondered why Ruger doesn’t chamber its little Model 96 lever action for the .45 Colt or, for that matter, the .480 Ruger. It’s simple enough; the geometry of the rotary magazine won’t handle cartridges that are fatter than the .44 Magnum. Either cartridge would require a complete redesign and probably would include a single-stack or three-round staggered magazine.

Montana X-treme
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