I've recently purchased a pre-war commercial sporting 98 Mauser by J. P. Sauer, chambered in 8x57mm. I have not slugged the bore yet to see if the grooves measure .323" or .318", but I have a question about the practical interchangeability of the two bullet sizes.
Based on the quoted post below, by JamesK in 2005, it would seem that rather than the diameter of the bore, the size of the chamber is the most important factor in firing "JS" ammo in a rifle. Do I understand this correctly?
So, even if I slug the bore at .318, might it be safe to shoot moderately loaded 8x57JS in the rifle, assuming that the throat is big enough for the case neck to expand? If so, how big is "big enough" for the throat?
Based on the quoted post below, by JamesK in 2005, it would seem that rather than the diameter of the bore, the size of the chamber is the most important factor in firing "JS" ammo in a rifle. Do I understand this correctly?
So, even if I slug the bore at .318, might it be safe to shoot moderately loaded 8x57JS in the rifle, assuming that the throat is big enough for the case neck to expand? If so, how big is "big enough" for the throat?
As for the "bore diameter" of Mausers, the bore was the same, .311" in our measurements. What was changed in 1905 was the groove diameter and the bullet diameter, from .318" to .323". Deepening the grooves allowed a barrel to last longer.
When the Germans converted Model 1888 commission rifles to fire the "S" bullets and marked an "S" on the receiver, they did not rebarrel or rebore. All they did was expand the chamber throat to allow case neck expansion; the barrels are still .318" groove, .311" bore. (They also closed off the bottom hole in the magazine and fitted clip guides.) I have fired WWII German GI AP and ball in them with no problems, but for obvious reasons will not recommend it. As far as I can determine no small bullet ammunition or M1888 en bloc clips were issued in the German service in WWI or WWII; the standard 7.9 (.323" bullet) was issued for all use, in the standard "stripper" clips.
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The 8x57mm Mauser itself has several names. In the civilian world, it is called the 8x57JS (J=Infantry, S=large bullet). In the German WWII military it was called the 7.9. There was a rimmed version for drillings, called the 8x57JRS (R=rimmed). The older rounds with the .318" bullet were called the 8x57J and its rimmed equivalent, the 8x57JR.
Jim