8mm Nambu Cartridge Conversion

[sheepherder]

Originally Posted by Sieger

I also enjoy shooting the Japanese Nambu Type 14, and own several of them. Though not a "Luger", they are really of quite good design and are quite accurate when handloaded properly.

Bob, I did a Search of this sub-forum to see if you had posted any of your Nambu handload data, and didn't find anything (only came up with six threads with Nambu in them, in this sub-forum)...

I still can't get any of the powder I'd like [4895, W231] but I have some Red Dot and Blue Dot left from before the freeze...

Do you have any loads for the 102gr FMJ Nambu bullet using Red or Blue Dot???

I was going to try a load for the 93gr 30 Cal Luger using Red Dot from a 1970 Lyman manual in my Nambu conversion cases...They list a low end of 3.9gr and max of 4.3...I may try 4.8gr to start, just a few to see if it cycles or if the primer flattens...Couldn't find any Red Dot data for the Nambu on the net...

[sheepherder]

Bob/Sieger's comment about the rim got me thinking, and I ran my 40 S&W cases on the lathe and turned the rim down to approx .042"...(from approx .052")...But when I ran my mixed bag of other brands/calibers, there was some variation, as much as +/-.004"...

I was using a live center and locating off the edge of the primer pocket...But they weren't all the same...Some had a tapered edge, some not so much...So my 'zero' wasn't quite right...

So to make a better 'zero' I turned a piece of Nylon down to fit in my tailstock Jacobs chuck with a small primer 'nub' [.175"] on one end and a large primer 'nub' [.210"] on the other end...

Now I clamp this mandrel in the Jacobs chuck, set it at zero, push a case up onto the mandrel and then clamp the neck in the lathe chuck...Case is centered and rim base is up against the mandrel...And now I can cut my rim...

Works much better! Variation is cut down to approx +/-.001"...

I would rather use Teflon for my mandrel...But I'm all out...

[Sieger]

Originally Posted by sheepherder

Bob, I did a Search of this sub-forum to see if you had posted any of your Nambu handload data, and didn't find anything (only came up with six threads with Nambu in them, in this sub-forum)...

I still can't get any of the powder I'd like [4895, W231] but I have some Red Dot and Blue Dot left from before the freeze...

Do you have any loads for the 102gr FMJ Nambu bullet using Red or Blue Dot???

I was going to try a load for the 93gr 30 Cal Luger using Red Dot from a 1970 Lyman manual in my Nambu conversion cases...They list a low end of 3.9gr and max of 4.3...I may try 4.8gr to start, just a few to see if it cycles or if the primer flattens...Couldn't find any Red Dot data for the Nambu on the net...

I haven't done as extensive work with the 8mm Nambu as I have the 9mm Luger, but a good powder for me was Unique with the Nambu. When I find the time, ha!, I'd like to try my favorite Power Pistol and SR 4756 powders with the Nambu, as I think they would do quite will in this case.

Also, start low with your above load, say 3.5 grains of Red Dot or so, and work up until the action will just stay open. By doing so, you will have established the bottom load of your relevant range. Carefully work up one tenth of a grain from there and note accuracy. Also, a hot load is not usually an accurate one, in most cases.

Go ahead and try the same 3.5 gr starting load with your Blue Dot powder, working up until the hold open catches to find the bottom of your range as note above. Blue Dot for me has always been a flame thrower, but with bottle neck cases it may perform a bit better.

Sieger

[sheepherder]

I ran across this powder chart for the 8mm Nambu in another forum...It was supposedly copied from the Midway site some years back...

I haven't seen anything like that on Midway now...

[rhuff]

I am not too sure how well the Blue Dot powder will work for you, but it is sure worth a try since you have some in hand. Blue Dot really shines when you load it up near or at max loadings. It is a magnum powder and likes to be loaded hot. I use Blue Dot in 357 Sig brass, and it produces superb velocity and accuracy. The only down side(to some at least) is the flash/bang that it produces. It is quite impressive!!!

[sheepherder]

Originally Posted by rhuff

Blue Dot...is a magnum powder and likes to be loaded hot.

I'm going to use the Red Dot first. Right now I'm trying to figure out this 3-die set, as it has no instructions and there is one die that I'm puzzled by...

[rhuff]

Was it originally a 3 die set, or has someone added a die, and forgot to tell you?? With your experience in things like making modified/reformed brass and reloading, I can't imagine what kind of a die has you stumped!! You have definitely peaked my attention.

[sheepherder]

Originally Posted by rhuff

Was it originally a 3 die set, or has someone added a die, and forgot to tell you?? With your experience in things like making modified/reformed brass and reloading, I can't imagine what kind of a die has you stumped!! You have definitely peaked my attention.

Right. OK, here goes:

RCBS die set as shown in post #5 above. First pic below shows all three dies in the set I received, disassembled. They are marked as follows, in order as shown -

[first die] RCBS 8mm Nambu Size # 170 on die body

[second die] RCBS 8mm N on ram; no die marking

[third die] RCBS 8mm Nambu Seat #370 on die body

Second pic below shows just the middle die, with dimensions as shown.

Here's the problem...The ram in the middle [expander?] die expands the cases so that a .321" bullet falls right in. Very good fit; I can feel the air rushing out the primer hole. The ram also has a taper leading to another expanding size which is a sliding fit in a 38 Special/357 Magnum case but does nothing to an 8mm Nambu case unless you push it down to the beginning of the taper, when it will give the case mouth a very slight bell...But if you expand the entire neck, there is nothing to hold a .321" bullet in place to crimp it...It falls inside...

Pretty much every book I have [including COTW] shows the Nambu bullet as .320", which is even worse...

I first thought the middle die was the accessory die for expanding the 38 Special case, but the entire ram slides right through & bottoms out...Without touching the 38 Spl case...So it's not the expander for making 8mm out of 38 Special...

I can just push the middle die ram down a slight bit in my formed cases, but then I get no bell...

So...WTF is this die for???

[Sieger]

Originally Posted by sheepherder

I ran across this powder chart for the 8mm Nambu in another forum...It was supposedly copied from the Midway site some years back...

I haven't seen anything like that on Midway now...

Hi,

Given my memory from 10 years ago or so, I doubt the Unique Powder load suggestions in your chart will even operate a T-14's action properly (hold open activated on last round).

If this is so, keep adding 1/10 of a grain, to the minimum load listed, until the action just holds open. You have then established your lower end base load, and can work up, very carefully, from there.

The gun rags have repeated, over and over and over again, that the 8mm Nambu is a sissy. Perhaps, it had to be loaded as a sissy, so that the inferior and weakly designed Type 94 Nambus wouldn't, simply, blowup.

Though it's certainly not a 9mm Parabellum, I'm not yet convinced that it needs to be a sissy when shot from a good, sound, Type 14 pistol, and would expect similar performance from it as from its European contemporaries (from which it was obviously, copied).


Sieger

[sheepherder]

The long-awaited, backordered 3-die set of RCBS 8mm Nambu reloading dies arrived today. Ordered 12/27/13, arrived 03/13/14.

There are a few slight differences from the used set I purchased on eBay. Nothing major. The expander die is separate, like my used set. The sizer die does not use the expander 'ball' like RCBS Tech Support sent me. So I'll continue to use my home-made expander die (I'll be listing this new unused die set in the For Sale sub-forum).

I have three different digital & dial calipers; they all read differently. So, the expander is either .3185", .319", or .321". Take your pick.

This set uses the setscrew locking rings. I really prefer the older split rings. Just my preference.

[Sieger]

Originally Posted by sheepherder

The long-awaited, backordered 3-die set of RCBS 8mm Nambu reloading dies arrived today. Ordered 12/27/13, arrived 03/13/14.

There are a few slight differences from the used set I purchased on eBay. Nothing major. The expander die is separate, like my used set. The sizer die does not use the expander 'ball' like RCBS Tech Support sent me. So I'll continue to use my home-made expander die (I'll be listing this new unused die set in the For Sale sub-forum).

I have three different digital & dial calipers; they all read differently. So, the expander is either .3185", .319", or .321". Take your pick.

This set uses the setscrew locking rings. I really prefer the older split rings. Just my preference.

Hi,

Years ago I experienced the same level of frustration with an RCBS set of dies for my 11mm Mauser rifle.

I finally gave up dealing with the Neanderthals and had a custom "M" Expander Die" made up. Ah, perfection, at last, was achieved!!!

By the way, having measured original, FMJ Japanese bullets from .320 to .322, I'm trying to figure out why this group of Neanderthals have given you an expander button ranging from only .3185 to .321: as the expander should be your bullet's diameter, plus a few thousands, to allow for brass snap back. Certainly, a proper expander die has got to allow for the adequate belling of the case mouth as well.

Just some thoughts.


Sieger

[rhuff]

I, personally, would not want an expander that was the same size as the bullet diameter. I usually try to achieve .003-.004in. smaller expander over the bullet diameter so as to achieve a good interference fit, and excellent neck tension. YMMV.