8mm Nambu Cartridge Conversion

[sheepherder]

I turned down another 1/2" x 20tpi SHCS to an expanding ram...It ended up .319"...With a slight taper for belling the case mouth...Seems to work pretty well...

...But I'm still thinking about Bingo...

[rhuff]

I believe that you are going in the correct direction with making a new expander/belling ram. I ran into a similar situation when I started handloading for the 30 Luger some years ago. My original die set (Lee 3 die set) would not function for me at all. The sizer die would not size the neck down sufficiently to give me any neck tension on .308in. bullets.

At first I thought it was that the expander/powder funnel was too large below the belling area, but that was not it. Anyway, I purchased an RCBS 30 Luger sizing die, then reduced the Dillon expander/ powder through die by .002in. and got sufficient neck tension on these .308in. bullets. I had to machine .040in. off of the base of the Dillon expander/powder die so that it would sit lower and give me enough belling for the case mouth. It works great also on the .309 and .311in. lead bullets. It surely had me scratching my head for a while.........bingo was looking good!!


Out of the 3 dies in the Lee set, I am using only the seating die. We live and hopefully learn.

[sheepherder]

Originally Posted by rhuff

At first I thought it was that the expander/powder funnel was too large below the belling area...I had to machine .040in. off of the base of the Dillon expander/powder die...

I'm confused (and bewitched, bothered, and bewildered but that's another story) about what a 'powder funnel' die is...Is this for some kind of progressive loading press, with multiple stations that revolve with each pump of the handle (or maybe motorized)???

I only tried progressive loading once, and discarded the idea forever. (I had a 6-station press but the turret was too wobbly; I had to shim the rear with a feeler gauge to keep it from cocking at an angle when you cranked the ram up/down...I think it may have been an RCBS turret press but I can no longer remember...) I don't like the idea of cranking out a round with every pump. I'd rather do 50 de-primes at a time; then size those 50; then prime the 50; then charge the 50; and finally seat the 50 bullets...I'll even run 5 or 10 through all the steps and shoot them off to make sure I've got everything right...I especially like a 50 rd loading tray to charge the primed cases 50 at a time...And look in and see if I have a double charge, or a half charge, before I seat the bullets...

On Lee dies, when I first started reloading, I once had a set that had the plating flaking off...

[sheepherder]

I primed several cases and charged them with 3.5gr of Red Dot. Bullet seated to an OAL of 1.244". Ready to try them out...

I may not try any more until I get another set of springs from Wolff...(see other thread)...

[Sieger]

Originally Posted by sheepherder

I primed several cases and charged them with 3.5gr of Red Dot. Bullet seated to an OAL of 1.244". Ready to try them out...

I may not try any more until I get another set of springs from Wolff...(see other thread)...

Hi,

Where did you get your O.A.L. figure, as it should mirror an original Japanese round, somewhat.

Nambus are not as touchy as Lugers when it comes to O.A.L., thank the slightly straighter grip angle for that.

Good luck, and do replace your springs with a fresh set of Wollf springs, as the metal in the Japanese springs is inferior.

Sieger

[sheepherder]

Originally Posted by Sieger

Where did you get your O.A.L. figure, as it should mirror an original Japanese round, somewhat.

From an original Japanese 8mm Nambu cartridge provided by Ed Tinker, and from data listed in Handloaders Manual Of Cartridge Conversions. 1.244" was the same in each case. Cartridges Of The World has it listed as 1.25"...Close enough.

Good luck, and do replace your springs with a fresh set of Wollf springs, as the metal in the Japanese springs is inferior.

Actually, my test showed no practical difference in the Nambu springs and the Wolff replacement springs.

I have no confidence in the Wolff replacement 'standard' springs which I received, as I commented on in my other Nambu thread. I placed an order tonight for their 'extra power' Nambu springs, which I'll test as I did their 'standard' replacement springs.

************************************************************************ ***********
In other news...

I had also emailed both RCBS and Lyman about different questions I had about their products. Lyman has not answered me about that #32362 bullet, but a CS tech at RCBS emailed me that they will send me out a replacement "expander/decap unit" for my #36404 die set...I had asked for the instruction sheet and explained that my expander was oversize for the Huntingtom .321" FMJ bullets...

[Sieger]

Originally Posted by sheepherder

I primed several cases and charged them with 3.5gr of Red Dot. Bullet seated to an OAL of 1.244". Ready to try them out...

I may not try any more until I get another set of springs from Wolff...(see other thread)...

Hi,

Then given a similar bullet nose contour, you should have a good starting place for continued A.O.L. experimentation.

Please also note that the Japanese were known to prefer short ogive bullets, leaving more of the bullet to actually ride on the lands. This was particularly so with their Arisaka rifles, the T-38 being, in my opinion, a simplification, yet refinement, of the Mauser action design.

Some golden daybreak, I'd like to design a truncated cone bullet for the 8mm Nambu, probably starting off with the DWM truncated cone for the 7.65 Parabellum as my guide.

Really, the 8mm Nambu and the 7.65 Parabellum both suffer from not having a decent selection of well designed bullets available to the handloader.

Regarding your powder, as soon as you get your feet wet with your new cases, I'd switch to the same True Blue powder you found so helpful in solving your 9mm problems, as the bottleneck cases should react particularly well to a slower powder.

Some fine day, when we can actually buy powder again, I'd like to experiment with the newer medium-slow/slow-slow powders to see if any of them are worth a hoot accuracy wise in the 9mm Parabellum pistol. Perhaps I'll be surprised, perhaps not, but the fun is in the experimentation and refinement of the various powders and other component parts of a load, always seeking that last little bit of perfection.

If you have the time to measure it, would you please give me the actual length of Ed's original Japanese bullet.

Thanks!


Sieger

[sheepherder]

Originally Posted by Sieger

Regarding your powder, as soon as you get your feet wet with your new cases, I'd switch to the same True Blue powder you found so helpful in solving your 9mm problems...

I haven't had any 9mm problems...I don't use True Blue (never even heard of it)...

Only problem I have had in the last year is getting powder...And primers...

If you have the time to measure it, would you please give me the actual length of Ed's original Japanese bullet.

As stated above, it is 1.244"...A rare instance of a book value being right on the actual value...

[Sieger]

Originally Posted by sheepherder

I haven't had any 9mm problems...I don't use True Blue (never even heard of it)...

Only problem I have had in the last year is getting powder...And primers...



As stated above, it is 1.244"...A rare instance of a book value being right on the actual value...

Hi,

I was looking for the bullet length, not the cartridge O.A.L.

My comments regarding powder selection above are still on exact point; though brainfarted in from another thread. Frankly, I'd be surprised if you get accurate groups out of Red Dot in this case and caliber, though I'm sure the pistol will function properly with the correct charge.

Please note that both the Nambu pistol and Arisaka rifle use the old British style Medford rifling: shallow, wide and with grooves usually oversized. This means that you can use oversized diameter bullets and still get away with it. .323 lead bullets are often used in the Nambu pistol, and quite successfully. Also note that when compared to a Luger, for instance, the Nambu has quite a bit of free bore built into its chambering.

Sieger

[sheepherder]

Originally Posted by Sieger

Please also note that the Japanese were known to prefer short ogive bullets, leaving more of the bullet to actually ride on the lands.

Here's a comparison of the two Nambu cartridges I have plus my conversion (pic attached)...

The lead-bulleted cartridge is headstamped 'W C C 6 6' and was bought from a cartridge collector at a gun show in the late 70's/early 80's for $1.00...Ed's cartridge has no markings...Mine is the 40 S&W conversion...

Lead - .407" rim .376" base .844" case 1.240" OAL .320" bullet
Ed's - .412" rim .411" base .861" case 1.244" OAL .320" bullet
Mine - .413" rim .410" base .866" case 1.246" OAL .321" bullet

The lead-bulleted cartridge has a pronounced semi-rimmed configuration...I have no idea what it actually is (original case)...I am measuring the bullet at the case mouth, it may be larger inside the neck...

[Sieger]

Originally Posted by sheepherder

Here's a comparison of the two Nambu cartridges I have plus my conversion (pic attached)...

The lead-bulleted cartridge is headstamped 'W C C 6 6' and was bought from a cartridge collector at a gun show in the late 70's/early 80's for $1.00...Ed's cartridge has no markings...Mine is the 40 S&W conversion...

Lead - .407" rim .376" base .844" case 1.240" OAL .320" bullet
Ed's - .412" rim .411" base .861" case 1.244" OAL .320" bullet
Mine - .413" rim .410" base .866" case 1.246" OAL .321" bullet

The lead-bulleted cartridge has a pronounced semi-rimmed configuration...I have no idea what it actually is (original case)...I am measuring the bullet at the case mouth, it may be larger inside the neck...

Hi,

It might just be an optical, but it looks like the thickness of your rim base is substantially thicker than Ed's original. This causes the extractor damage mentioned previously. What is the original rim base thickness? What is your rim base thickness?

Sieger

[rhuff]

Originally Posted by sheepherder

I'm confused (and bewitched, bothered, and bewildered but that's another story) about what a 'powder funnel' die is...Is this for some kind of progressive loading press, with multiple stations that revolve with each pump of the handle (or maybe motorized)??

Sorry that I wasn't very clear on my description of things. Yes, I am loading my 30 Luger brass on a Dillon 650 progressive press. At station 2(after sizing and priming) the powder funnel enlarges the case neck and bells the case mouth, along with adding the powder charge. At station 3, the powder check die checks for the correct amount of powder in the case. Then on to seating and crimping. A total of 5 stations in all. It is a self indexing press.