8mm Nambu Cartridge Conversion

[sheepherder]

I also made up some 38 Special cases without cutting the extractor groove. But I needed to expand the cases, as the OD was [IMHO] excessive for the 8mm chamber - Something like .030" smaller. I've been told that unexpanded 38 Special case used for 8mm Nambu could/would split when fired. To counter this I made up my own 'expanding die' out of 1" steel rod.

[pic 1]

Turned down to ~ 7/8" diameter. The die body was also drilled & internally threaded to 1/2" x 20tpi for my 'ram'. The die body was also drilled for 3/4 of its length to 27/64" to contain cases expansion.

[pic 2]

Threading the die body OD to 7/8" x 14tpi.

[pic 3 and 4]

Turning the 'ram' out of a 1/2" x 4" SHCS.

[pic 5]

Expanding die in RCBS press, cranking out expanded 38 Special cases.

[pic 6]

Close-up of expanding die.

[pic 7]

Some expanded cases.

[pic 8]

One of our members mentioned having reloaded 8mm Nambu ammunition that was made from 40 S&W brass. I was able to filch some once-fired 40 S&W cases out of the brass barrel at my local club for conversion.

Using the fired cases, I de-primed them using my 44 Special sizing die with the 22-250 decapping pin. I left the case rim and extractor grrove alone.

I've read of extraction problems with the 40 S&W case conversions. The 40 S&W case is oversize for the 8mm Nambu specs, so I swage these cases. These cases were all right at the ~.415" base measurement; I want .407" - .410". I use the 30-30 Winchester sizing die again to resize the cases, same procedure as described previously for oversize cases.

My 40 S&W cases are now ready for neck forming.