Here is the process I followed to convert 357SIG brass into 8mm Nambu ammo. I have lots of Speer brand 357SIG once-fired brass I bought on sale almost 8 years ago. 8mm Nambu reloadable brass cases are hard to come by and expensive when found. These reformed cases will function just as well.

The first step is lubricating the brass and then running them through the full length 8mm Nambu sizing die. I used my Forster Co-Ax single stage press for the task and even with its compound leverage it took quite a bit of oomph to do, times 50. But none got ruined.

Step 2 was to trim the necks back to the correct length as reducing the diameter from .355" to .320" made that excess brass squeeze the neck longer. But that task was made easier by the Bosch tool which also performed the inside/outside neck chamfering process to remove burrs.



Step 3 was, at first, riddled with fits and starts...the biggest was what was the best way to chuck the case so the body can be reduced from the SIG's .427" to the Nambu's .407", or a reduction of .020". I practiced on some nickel-plated SIG cases that were ready for the scrap heap. I won't bore you with the details, but a .320" mandrel inserted to the bottom of the case and a pilot inserted loosely into the primer pocket did the trick. The 3 jaw chuck didn't even mar the soft brass of the case neck and the pilot spinning at 800rpm didn't oversize the primer pocket hole...so far, so good.



I could have cut the pilot a lot shorter, but I wanted plenty of room and it didn't seem to hinder the process any.



Doing 50 of these cases took about 1 hour once I got the stops set and got into a rhythm. I chose this style carbide bit because of the limited space of the extraction groove...I didn't want to touch the case rim, only the body.



Parent 357SIG on right. You can see I didn't cut off that much material but it certainly evened out the body thickness which was probably another effect of the resizing process. I checked every single case in the Nambu's chamber to be sure of a good fit.



The finished product. The remainder of the first batch of 50 were shot and are waiting to be reloaded once Big Brown truck arrives with more Graf TMJ bullets. I was so pleased with how these SIG cases turned out that I did 50 more! So, these 100 reformed cases plus the original 50 HDS cases should do me for awhile.



Resizing was the last step...I just wanted to be sure the case neck was squeezed down to hold the Graf bulk .320" 84gr bullets tight. I didn't even bell the case necks...the inside chamfer on the neck and the bullet's partially rounded heel made bullet seating a breeze. They fed, fired and ejected just fine.

I measured the case capacity and these SIG cases have 1.4gr less than the HDS headstamped brass. I'm not exactly sure what fps difference it caused because I switched from Remington primers to CCI...but the speed was in the same ballpark, average ~1060fps.

Now the cast boolit on the left presented a problem I never encountered before. The slide wouldn't go into battery so my first thought was that the boolit was just seated too long...nope. It turns out the case neck was too big in diameter, yet those boolits are only .321" or .001" larger than the jacketed. I ended up pulling the decapping rod from my resizing die and running these loaded rounds partially in, to just squeeze down the neck. Doing so meant I didn't have to re-lubricate the entire case. Believe me, I was trembling a little on the first pull of the press handle...I never tried performing ANY operation on a loaded round before. But I'm still here to tell about it, thankfully.

I reduced the powder charge from 4.5gr to 4.1gr of W231 due to the heavier boolit. Once this extra step was done they also fed, fired, and ejected just fine. But I will buy no more 102gr cast boolits for this Nambu from AmmoDepot. I plan on setting up these Nambu dies on my Dillon RL550B progressive press (which I already use for the 357SIG)...one trip through and a loaded round is ready for the chamber. I don't need the extra aggravation of cast boolits not chambering.

P.S. I'm going to use the lathe to decrease the diameter of the 8mm Nambu Redding neck expanding die but just on the shank...leaving the belling function intact...and the necks really need belling to start those cast boolits. It measures .3185" now and obviously is causing my cast boolits to not chamber...of which I have 400. Damned if I'm going to resize all of the necks again once the bullets are seated.

I'll try taking off .001" to see if that makes a difference.

Well, that was a fun, worthwhile and educational project.

P.P.S. UPS dropped off more of Graf's bullets yesterday so I picked 7 pieces of this reformed brass and loaded and fired each 6 times...no problems with weakened case body because of cutting .020" from wall thickness. Remember, this SIG brass was designed for 40KPSI. 8mm Nambu is probably half that pressure. So everything's good to go!

Wow, work of love for a Nambu.

I'd say you qualify for a reloading black-belt.

How do you like the MicroLux?

quote:

Originally posted by craigster:
How do you like the MicroLux?

Peachy, although I have nothing to compare it with except an Ammco brake lathe at work. But that comparison is a real stretch.

quote:

Originally posted by fredj338:
Wow, work of love for a Nambu.

I don't consider it work, it's my hobby. And I like my collectibles to pop some caps on a regular basis. Otherwise why have them?


I ended up removing .010" from the belling die's shank, to a final diameter of .3085". (I blued the bare metal to prevent rust.) Resized brass is now a slip fit.
Unfortunately, it didn't help...those cast boolits plus the thickness of the neck is just a bit too much to allow the slide to lock up tight. Drat! Perhaps my Type 14 Nambu pistole has the tight 'match' chamber?

I wouldn't doubt this pistole is being shot more now than in WWII.

In case you have not seen my other post concerning what this ammo is intended for, Click Here.