Belted Magnum and similar-
diameter cases, an average of about 15/10,000-inch.
I have found that if the initial fi ring
generates only about half this much case rim expansion, then repeated use of the same load is not apt to eventually loosen the primer pocket. The case head hard- ens with each such use and therefore expansion progressively diminishes and eventually ends. If initial-use expansion is not too great, repeated use of the same load will not cause enough total expan- sion to loosen the primer pocket enough to cause a problem. How convenient! DEALING WITH THE HORNET CASE The Hornet represents a special
case (all puns are always intended). Hor- net case heads are so weak (thin between primer pocket and rim cut and often also relatively soft) and usable capacity is so limited that we really do need to know where we are in terms of actual pressure generated by any given loading, and the only way I know to know that is to keep increasing the charge until the case begins to fail. Trial by fi ring, as it were. (Please use extra caution when working with any gun that lacks complete sup-
port of the case head.) In chamberings based upon the
Hornet, I have found that, often, a load that seems perfectly normal is converted into a case-destroying load by increas- ing charge weight only 0.2 grain! What this means is that you could well be us- ing a load that seems perfectly normal but that, in reality, is only a few-tenths grain from being potentially dangerous. As an example of how this could
lead to trouble, assume the situation described above and then imagine what might happen when you begin to use propellant from a new can that happens to come from a production lot that burns a few percent faster than the propellant you had been using. (Normal lot-to-lot variations in propellant burn rate are often plus-or-minus 1½ percent, sometimes greater.) Or, consider what could happen when you begin to use those loads on an unusually hot day or when the barrel is fouled unusually heavily, etc. LIMITATIONS AND DANGERS Now, for one bit of, perhaps, so-
bering news: Case head hardness varies among cases in any production lot, more
so from one production lot to the next, considerably from one case type to the next, and from one manufacturer to the next. Some are so soft as to be essentially useless to handloaders; others are so hard as to render case head (rim) ex- pansion a useless tool and a potentially dangerous crutch! As perhaps the ultimate example
of the latter, consider what Bill Falin observed while developing loads for the 350 Remington Magnum at Accurate Arms. He inadvertently discovered that the Remington cases he was using had unusually hard heads. Intrigued, he set out to measure how much pressure those would take before permanently deforming. At approximately 100,000 psi
(which would be apt to catastrophi- cally destroy some factory-chambered 350 Remington Magnum guns with one shot, with the potential to kill the shooter or bystanders), Falin lost his nerve. He was concerned that if he persisted in pushing test pressure ever higher, he was apt to destroy a transducer and related components worth many hundreds of dollars. (The
AIMING GUIDE
centerpointoptics.com TRAJECTORY
ONE RETICLE with a WIDE RANGE OF
Page 94 July — September 2011 BULLET/LOAD COMBINATIONS! ONE SCOPE
By matching ammunition ballistics to placement of the crosshairs on the reticle, the need for estimation is eliminated. TAG reticles accommodate distances from 100 yards to 600 yards.
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