Sunday, January 12, 2003

I was posed an interesting question about the varying rim diameters of the 7.65x53mm Mauser cartridge. Since I have cases made from many different brands, and Norma, Argentine commercial (albeit made by the national armory), and the new Frontier as sold by Graf and Sons, I've measured and posted the results here:

Argentine commercial - .473"
Norma 7.65x53 - .473"
Frontier 7.65x53 - .468"
PMC 8x57 reformed - .468"
RP 8x57 reformed - .467"
FC 8x57 reformed - .468"
RP .30-06 reformed - .468"
FC .30-06 reformed - .470"
Win .30-06 reformed - .466"
FC.270 reformed - .470"

Interestingly, while this got boring to do, it pointed out a couple of interesting things:
- .473" seems to be the standard we should "shoot" for. There's a reason the Argentine is that size.
- .007" inch is the maximum difference between cases but all function without problems in my M1891 carbine.
- 8x57 is the easiest to reform (simply lube, run in the die and trim to length, then fireform), it may NOT provide the best parent brass for some users.
- Winchester .30-06 brass has the smallest rim diameter of commercial .30-06 brass available to me.
- My military .30-06 cases are buried so deeply in my reloading area I can't find them!

I think that it just doesn't matter that much. Once fireformed to the chamber of the rifle you are using, it will work very well indeed. And I think it should be formed to the chamber of the particular rifle you're using as the chambers seem to vary, sometimes widely. The only other consideration is whether or not the extractor will be able to grab the rim.

Additionally, I was asked about the .30-06 vs 6.5x55 case heads. Interestingly, all case heads .30-06, .270, 8x57, and 7.65x53 consistently measured .470 +/- .0005" and all the 6.5x55 measured .480 +/- .0005". This is to my mind one of the critical dimensions to look at when reforming. While .470" dia case heads MIGHT function in the .480" chambers they certainly won't last long.

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