Greetings Again,
Cold and windy today (old age pensioners are sensitive to this) so I dug out the article mentioned above which appeared in 1987. The cartridge was the .240 Gibbs. This is the .25-06 necked down and the shoulder blown forward. Roger Stowers, who wrote the article, started with what he thought was a start load of 49 grains of IMR4831 behind the 105 grain Speer spitzer. Blown primers appeared straight away. Later he found that elevating the muzzle to settle the powder next to the primer eliminated the problem so to me this was an ignition problem. Over time he included H4831 and IMR7828 with the same results and finally increased the powder charge which cured the problem. He also tried seating the projectiles with much more jump to the rifling which had the same effect.
So to summarise the problem was with slow powders that did not fill the case with cases that had very large capacity for the bore. Roger did not mention what primer he used but most data for the smaller .240 Weatherby use magnum primers. I wonder if these may have helped.
Regards Grandpamac.
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