Might need an arbor press.  While you can reduce jacketed bullets in this manner, the soft lead core can loosen.  The copper alloy jacket will tend to spring back but the lead won"t.  Also, those Lyman size dies are set up for lead alloy..jacketed will come out larger than stamped size.

I looked at this a bunch a few years ago, and finally bought some already done.   

The information I gathered at the time said that accuracy was poor, unless you sized down smaller than the desired diameter, and then used a swager and die to bump up the size to what you want. 

Sizing down loosens the core, and the jacket springs back more than the core.  The resulting misbalance affects accuracy.

Bumping it back up stretches the jacket and forces the core into it tight, and the jacket springs back more than the core, essentially compressing it.  This restores the accuracy.

What I also read was that shooting .323 usually works in a .318, unless the neck is too tight.  The bullet just swages down and works.  Start with a bit of a reduced load to try it, of course.   

I haven't shot my J bore mauser enough to really test any of the above.  I lost interest in it when I finished working on it.

ssdave wrote on Feb 18^th, 2024 at 11:13am:


If I remember correctly, many of the older .318 bore rifles had the throats re-cut to accept the newer cartridge. I am guessing it may have incorporated a longer, tapered throat to ease the pressure as the larger bullets staged down

I collected 1888 Commission Rifles (the first 8mm) for a few years and have about 8/9 of them, including the Turk, rebarreled ones so, I studied them, in those years. 

The 8mm, has a very long throat. It is about .42°, originally made for the very long, round nosed 223gr bullet. Originally 7.9 bore x 8.1 groove (J bore). In, I believe 1905 they increased the groove to 8.2mm (S bore) and started using the 154gr spitzer bullet.

A lot of people think that the J bore rifles were rechambered  to shoot the Spitzer and "S" marked but, they were marked "S" after they were tested, with a gauge to insure that they would chamber the "S" bullet.

The "S" bullet has a very short groove diameter band, about .23 so, in the long throat, it will swedge down easily and so will lead bullets of any type.The problem for the "J" groove barrels, are long .323 bearing band bullets, like the 198gr spitzers or the Speer 200gr bullets

frnkeore wrote on Feb 19^th, 2024 at 3:54am:
my understanding was a combination of long bearing surface and shallow grooves in the I or J 8mm, caused rapid barrel wear. To solve the problem the JS rifling was deepened and a 154gr
Bullet was adopted.
Mike