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Old May 8, 2006, 10:33 PM   #1
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Correct 30/06 base diameter ???

In considering potential wildcat cartridges, it has come to my attention that there seem to be many different base diameters listed for cartridges based on 30/06 brass. The most common seems to be .470, but I have seen numbers from .465 to .473 listed by different sources. I mic'd a few cases that I fired in an original 1917 Enfield, and they measure .465. But is that just a minimum on a tight chambered gun? Can a chamber be reamed to .473 or maybe even .475 at the base, and then fire form the brass to that dimension? How big is too big before the brass would tend to split? I intend to use straight wall unformed 30/06 basic brass to start from. This may seem insignificant, but I'm working on a wilcat where every .001 will count.

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Old May 9, 2006, 12:20 AM   #2
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.473 is the max cartridge/min chamber spec. .465 is a typical actual cartridge measurement. If you load hot enough to expand the head, the primer pocket expands right with it. That's one of the classic signs of an extreme overload.

Candidly, I don't think there is anything you can do with the .30-06 case that someone has not already done.
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Old May 20, 2006, 10:38 AM   #3
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Yep. It bears repeating - - -

All of what Leftoverdj wrote above, especially the part about, "Candidly, I don't think there is anything you can do with the .30-06 case that someone has not already done." The basic case has been around since 1903 and wildcat experimentation probably began even before the 1906 version was adopted.

This is the centenial year of the fine old cartridge. Perhaps my stodgy old imagination has malfunctioned, but I can't envision anything further that CAN be done with the basic .30'06 case. New bullets, new powders, sure - - We've seen significant improvements in these, even in the past ten years.

To expand on the base diameter theme, though - - Three loading manuals with cartridge drawings, plus Barnes' Cartridges of the World all agree with the basic 0.473 inch dimension. Not surprisingly, since they are all direct descendants, the same is true of .270 Winchester, .35 Whelen, .25-06, .338-06, 8mm-06, and heaven knows what else. Oh, yeah -- the .308 Winchester and all of ITS modifications. I won't count 'em all up right now, but I imagine that the basic '06 hull is parent or grandsire to at least a dozen others.

All the above notwithstanding, I'm honest enough to admit I'm interested in any developments you work out. Please keep us informed.

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Old May 20, 2006, 12:55 PM   #4
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30-06 Base Diameter

Realizedthat I had a dial caliper right here in my desk, a shiny unfired 30-06 cartridge across the room. Result = .465 " Case is marked LC68
on head.

Last edited by cuate; May 20, 2006 at 12:56 PM. Reason: left out something
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Old May 20, 2006, 01:18 PM   #5
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Get P.O. Ackley's "Handbook for Shooters and Reloaders" first. I doubt that you will come up with anything new that hasn't already been tried
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Old May 20, 2006, 01:56 PM   #6
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30-06 case heads vary as much as anything else. Most domestic brass will hover around .465" and firing that in a .473" chamber will result in a pronounced case bulge. If you are contemplating a custom chamber, take a fired case, FL size it, measure the base and shoulder, and have a reamer made that is .003" larger. This will give you a nice chamber where brass will last forever, won't need any trimming, and shoot more accurately than factory.
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