8mm Nambu Cartridge Conversion

[sheepherder]

Here are the cases that have been swaged or expanded. They are -

38 Special
375 Winchester & 30-30 Winchester
25 Remington & 32 Remington
40 S&W

These are now all straight-walled cases. The next step is to form the case necks in the RCBS 8mm Nambu sizing die.

[sheepherder]

Forming the neck.

RCBS 8mm Nambu 3-die reloading set. This is an older set, and the seller included an RCBS #25 shell holder. Nothing special here; lube the case liberally and run it through the RCBS 8mm Nambu sizing die with de-priming pin removed.

[Pic 1].

40 S&W in press.

[pic 2]

38 Special in press.

[Pic 3].

Trimming OAL to ~.862".

[Pic 4]

The various cases neck-formed but not yet trimmed.

[pic 5]

An experiment using a suggestion by a member in another thread (which I can't find now; sorry!), to power trim the cases.

[pic 6].

Finished 40 S&W case converted to 8mm Nambu and ready to reload.

[pic 7]


Notes

- The 375 and 30-30 Winchester cases were the most difficult to form & neck
- The 375 and 30-30 cases need the primer pocket reamed; the rest don't
- Winchester brass is softer than Remington, R-P, and military
- The rifle brass has thicker case walls, thicker base, and large primer
- 38 ACP/38 Super cases could also be expanded to form 8mm Nambu in the same way as the 38 Special. No groove need be cut and the rim need not be trimmed. I did not have any so there are no pics/comments.
- I test fit about 1 in 10 in my Type 14 Nambu; they all fit; bolt closes; extractor engages.

Conclusions

While many cartridges can be used to convert to 8mm Nambu, I found the 40 S&W to be the easiest.

The RCBS 36404 3-die set seems to be the best for forming & reloading.

In a surprise move, the president of our gun club presented me with a bag of 40 S&W once-fired brass last night. What a guy!