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If it is necessary for rimmed and belted cases to be "headspaced" on the shoulder, how come the headspace gauges are only short plugs and not full length.
As to case separation, I too have had separation in a .303, but it was due to excess headspace, and I suspect yours was also. Note the disclaimer in what I wrote. I said "if the headspace is correct", the case will blow out to fill the chamber instead of case separation taking place. The pressure expands the thin front of the case outward and forward without stretching the case enough for separation. Separation is caused when pressure sticks the front of the case to the chamber walls, but the bolt can move back enough to allow the rear of the case to pull back and tear the case apart. I suppose it could happen some other way; I know of none, but am willing to be educated if someone comes up with a reasonable explanation (not just "it happens").
As to .35 Remington, one of the big PITAs as a gunsmith, was the parade of guns in that caliber (mostly Marlins) that had erratic firing. It took a while to figure out that a chamber that was even a bit "loose" (cut with a new reamer, I guess) would allow a slightly undersize cartridge to "cushion" and cause misfires. The occurrences were random. Sometimes, we could correct the problem by fiddling with the firing pin, other rifles had to be sent back to the factory.
Jim
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