Reloading dies for .318 J-bore 8x57 mauser

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Potashminer

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So, there were two bore diameters used in the German cartridge known today as 7.92x57, aka 8mm Mauser, aka 8x57 - so the 8x57 I (or J) cartridge. I would like to know if the "J" bore (.318" bullet) cartridge requires its own set of reloading dies, compared to the "S" bore (.323" bullets). I presume so, but do not know. And then, if specific J-bore sizing dies are needed, any clues or leads where such things can be found today?? Any help appreciated!

Plan "A" seemed too easy - apparently can order custom die from RCBS - Group G - #56658 - per the Huntington website, $US143 plus shipping, etc. I am sure. So, am hoping there is a Plan "B"??? As a check, the expander ball in my Lee "8x57" reloading die set mikes about .320", so that is not going to work, directly, although the die should take care of FL sizing the body... Even if I turned down the expander to sort of .315"-.316" or so, I doubt the die will squish the neck down far enough??
 
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One way to find out........remove the die stem /expander from the sizing die.Run a lubed brass FL sized.Switch to the seating die and try to load a dummy round.If it grips the .318 bullet secure then I'd spin the expander in a drill with sandpaper to reduce the diameter as you mentioned.I have loaded .308 bullets in brass for the SKS doing the same thing.See what happens.
 
Maybe getting ahead of myself about dies, as the bullets have not even been mailed to me yet - but for sure that is first thing that will happen - a fresh PPU 8x57 brass into that Lee FL die, without an expander, and see what happens. Gotta try it to know, for sure!!!
 
Update -11-Sep-2021 - finally just did try it. - I have a Lee 8x57 Mauser die set. Set up FL sizer die in Rockchucker press - removed the expander. Used a brand new factory PPU 8x57 case. I took a Woodleigh .318" "J" bore bullet and just so able to slide it into a new (unre-sized) PPU case with my fingers - I would call it a "snug" slip fit. Ran a new case into the FL die - did not actually feel or hear any re-sizing going on - but now I can not push that bullet in with fingers - so, it is close. Would not have a lot of confidence to be able to hold against recoil though. This Lee die set comes with a Factory Crimp Die - if I set that up so the little collets close up tight, much smaller than the "re-sized" neck - so quite certain that FCD would put a crimp into a case with .318" bullet - would be a "barely just crimped" thing though - with a skinny neck case might not get anything...

Turns out the rifle had a "JS" bore - .323" bullets - so no actual need anymore for the "J" bore - .318" - to work. But, now I know...

But I still do not know if a 8x57JS case neck with a .318" bullet fitted and crimped, will fit into a 8x57J chamber or not!!
 
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I special ordered an RCBS dies set for my old .318" 8x57JR Drilling. ( rimmed version of the same cartridge you are referring to) They worked perfectly but I'm sorry I don't know the exact answer to your question. I have read of some die sets that come with both expander plugs, much like some dies the are made for the 7.62x39, with both .308" and .310" expanders for the same FL die. But I do not know of a source of dual purpose 8x57 dies. I did load 8x57JRS cases with .318" bullets and used them in that drilling, because I had very few cases that were headstamped with the correct 8x57JR designation. The case neck thickness ( RWS cases) is identical, as long as it is sized down to the proper internal diameter to hold the bullet they will shoot OK in either chamber.
 
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