Originally Posted by Max Heat
Hmm, I thought the 30 carbine (kalashnikov, or is it kalishnakov?) was 7.62x39, the .308 was 7.62x51, and the 30-06 was 7.62x57. But according to chuck hawk, the 30-06 is about 10 grains more than that. And the x57 round does appear to be the 7.21x57 (7mmx57) mouser case. Maybe THAT be the .284 case you refer to with the 22-284? I have decided to put this on the back burner and concentrate on getting some maximum barrel into my ultra 7 for now, anyways.
you have to go back to the very late 19th century to see that Paul Mauser came out with a 12mm (head diameter) case that was 57mm long. Later Springfield stretched that same case length to 64mm. This same case has been stretched and also shortened by other folks later. I think the 6BR is the shortest, and maybe the 270 Winchester is the longest version (or 280?). To the best of my knowledge the 7.92x57 Mauser case started it all in that case family.
Seven millimeter wise there are a gazillion of them! All the way from the 7mm TCU to
the 7mm Ultra mag. Efficiency wise the 7mm TCU is probably the best followed closely by the 7BR. After you get past the 280's and 7mm Remington mag (and Weatherby) you start to see serious diminishing returns for the efforts involved. The .284 is a good round, but the .280 is much better. Parker Ackley really like the basic 7mm Remington mag case as well as the 7mm Weatherby mag. Then you also have the 7mm WSM case that fits in most short actions nicely. Ackley felt the case capacity of the 7mm Remington mag to be about the max the bore could use unless you were shooting very heavy bullets. Then the Weatherby would take over. Yet both are only a fraction faster than the plain jane .280! The 57mm case length has gone thru various steps all the way out to .338, and probably .358 if I really looked hard. The 7x57 Ackley improved is well known as a great round that is only slightly slower than the .280, but uses a lot less powder. The .257AI necked up to 7mm is simply the 7x57 improved (or vise versa). I'm seriously thinking about the same round in 30 caliber. Ought to flat smoke the .308 in every way. My idea is to build a stretched .300 Savage, but with the .010" taper that Ackley used with the 30 degree shoulder that Savage used.