The .404 Jeffery is a tad bigger than you've specified (0.545 inch diameter at the web), and the 8x68mm S is a tad smaller at 0.5236 inch. This is larger than an H&H Magnum case with the belt (0.532 inch) turned-off (to about 0.515 inch across the web).
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<br>The 8x68mm case is 2.658 inches long. My .340 Howell Express uses the 8x68mm case but with a longer neck than you've specified.
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<br>Consider a longer neck (assuming that you intend to use long bullets). In considering neck length, the length of the bullet is more important than diameter. For lack of an established term for the crucial concept here, I've coined the term "socket engagement." This concept is more important for good cartridge performance than I've seen anyone else recognize. To get a quick hand-hold on it, recognize (for illustrative example) that while you can set all the fenceposts you want to, two feet in the ground, and get along just fine, you can't expect that socket engagement to be enough for a flag pole or a telephone pole. And a skyscraper has to be sunk several floors to be stable. After a while, the increase in socket engagement that you get with a longer neck (for the established case length) is more important than the slight loss in case capacity with that slightly shorter body.
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<br>I wouldn't use a shoulder steeper than 30� and would be careful to retain a good body taper to avoid having feeding problems. Popular folk-lore theories that favor minimum body taper or even cylindrical bodies have not proved their worth in use, while there's a substantial body of frustration with the difficulty of feeding cases that don't have enough body taper.
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<br>When I get my AutoCAD problems taken care of, I'll do up a drawing for you. The .338 Bin, as I "see" it now, should give you all that you'll ever need or want from .338 bullets.
