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ary 1957), letters started pouring in from "poor men" who wanted more Magnum. Most of them were already working on rifles for the new cartridge, and wished to discuss new loads and bullet weights to serve their special purposes.
Among the lot of nice and interesting letters, there were quite a few wishes for a bigger caliber, and there seemed to be an open door for further experiments. Now, in the way of wildcats, there actually isn't much that has not already been tried; but a study of the 1957 line of commercial calibers showed a definite gap in the 9 mm class. There were plenty of standard-length rifle actions on the market, but no commercially made cartridge that satisfied the wishes for "something more powerful than the .358 Winchester, but still not as big as the .375 H & IT"
Actually, the way of making up this missing link was quite obvious, and a couple of hours of work now and then in between lots of other jobs soon produced the new thing.
There were a couple of calibers to choose between in designing a new "Poor man's Magnum," but since most gunbugs live in the U.S., I found it most practical to utilize the .358. The European 9 mm's are harder to get in America. There were a couple of cases to choose between too, but both for the action's sake and for that of the performance requested, the .375 H & 11 belted case seemed to be the thing. This case also has the advantage of being available in cylindrical state, doing away with expensive and elaborate fireforming.
Kvale gives new shell figures in millimeters, may be changed to inches.
The case shape was hereby nearly given. To ease "manufacture," instead of a fancy shape leading to the discard of 50% of the cases in forming, a straight cone for the shoulder was chosen, with a good, sensible shoulder angle of about 25 degrees. Then we chose a reasonable neck length to give a steady hold for the bullet. The head of the case was left unchanged.
Of course, it is also possible to "open up" a small caliber to form a bigger one. However, a cartridge case is always drawn to a precisely pre-determined wall thickness at the open end before necking operations are started, so that, when necked and calibrated, the correct amount of material remains at the front end. Opening up a case to a caliber appreciably larger than the one for which it was made will therefore weaken the finished product, since there may not be enough material in its original neck to permit the necessary wall thickness when stretched. It is always easier to arrive at the desired caliber from the other direction. Excessive material can be done away with by a slight inside reaming of the finished neck.
I had aimed at a velocity at 12.5 meters of about 835 meters per second for my new cartridge, using the 250 grain .358 caliber
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