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357sig brass to 8mm Nambu

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Zeliard
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357sig brass to 8mm Nambu

#1 Post by Zeliard » Thu Jun 29, 2017 11:07 pm

Originally posted by 1Blue.

NOTE: While I don’t normally edit reposts (except for occasional typos, and usually not even then), this one has had the following edits performed: Posts combined, images reordered to flow top-bottom instead of bottom-top, first step about depriming .357 sig cases moved closer to top of article, and references to starting from the bottom removed.

The Internet can be a great thing. I had given up on trying to make 8mm Nambu from 38spl or 40 brass. Then recently I was trading brass with a new friend I had met on the Internet, when he asked me what I wanted? I responded, as a lark, 8mm Nambu. His reply was ok, I have some formed from 357sig. I about fell over. When I received it, I was very surprised how great it looked. It fit correctly in the Nambu shell holder, etc. So I had to learn how he did it. I would like to share it here so fellow Nambu owners can fire their pistols a little more often.

Remove the primers from the used 357 sig brass. I have a Lee universal decapping die.

Then, using an O ring single stage press, a 30-30 sizing die and a bullet pusher from a Lee 358 sizing kit.I bought this directly off the Lee site as a replacement part. Using some Imperial sizing wax, coat the outside of the 357sig case and push it about half way into the 30-30 sizing die. It requires some force but will go in. Then using a long bolt that clears the case mouth and makes contact with the case base, pound it out. One good rap works.

Next swap out the 30-30 die for the Nambu sizing die, take out the decapping pin, reapply some Imperial sizing wax and force the case up into the Nambu die. You need to take out the decamping pin because you'll notice the flash hole is smaller after running it through the 30-30 die. Also you will note that after the 30-30 treatment the brass will fit properly in the Nambu shell holder. If you get too much resistance pushing the brass into the Nambu sizer, stop and back it out! You don't want a case stuck up in your die. Apply some more wax and reinsert.

Finally take the case out and trim it to size. Drill the flash hole out to spec. Your done. Free 8mm Nambu brass. I'll post pictures when I get home.

If you get a band around the bottom of your case after running it through the 8mm sizing die, try pushing the case a little further up the 30-30 die.

Now when I'm at the range and see 357sig, I'm picking it up! Loaded Nambu runs about a dollar a round. My cost is now:

Brass - free
Primer - .03
Bullet - .14
Powder - .03

Here is my temporary loading bench. I would not recommend this setup for reforming brass. But it works in a pinch. My reloading bench has only enough room for my Lee cast turret press, smelter and Star lubrisizer. Since reforming cases isn't something I do all that often this works.

Workmate turned reloading bench.

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OK, I'll start with some pictures. My camera and photography isn't the best. A 357sig case, a formed 8mm Nambu case from a 357sig case and an actual Nambu round. The Nambu round is HDS 8mm brass. I wanted to show it for comparison. So I'll start here. I'll post pictures of my press bolted to my workmate saw horse and performing the first step of resizing the brass including the base. Then I'll show forming the case in the Nambu dies, trimming the case, making sure the flash hole in the primer pocket is the proper size. Then finally reloading the final product and compare that to this same pictured Nambu round. So please bear with me, it will take me a few days to set everything backup and take pictures. Whoops forgot to mention the formed case has also had it's mouth flared, so it looks a little wider, forgot to mention this step. Nuts, I forgot the first step. De-prime the 357sig cases.


Here are three cases. From left to right is the 357sig, a formed Nambu case from 357sig and a Nambu 8mm loaded round in actual Nambu brass case.

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Same cases showing the middle case's 357sig head stamp

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Comparison of the 357sig and the actual Nambu round

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O Ring single stage press. Note the bullet pusher in the press ram. I bolt this directly to my Workmate when I need to use it. There isn't enough room on my reloading bench. So I will set it up and post pictures later.

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30-30 die, case knock out bolt and a bullet pusher from a Lee 358 bullet sizing kit.

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Here is the Imperial case forming wax. You'll be amazed how little it takes. You need a good case lube/forming wax like this. Be patient, go slow, stop if you feel extreme resistance/binding. Especially during the forming step with the Nambu sizing die. Shearing off the base rim, leaving the brass stuck in your Nambu sizing die is the pits. Go Slow, don't just cram it in.

You can buy this from various sources, Midway, Grafs, etc.

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Ok, let's get started. With the 30-30 sizing die and using the Lee bullet pusher begin by inserting the 357sig into the die. Make sure you have removed the primer. I usually insert the case about half-three fourths the way in, then pound it out. I use a little more lube/wax and finish inserting the case all the way into the die. Including the base. It resists and then slips in. It should be about 3/8 of an inch into the die. Then pound it out. Couple good whacks works.

Step one.

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Here is the case about 3/8 of an inch in the 30-30 die.

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Now take a look. The 357sig has started it's transformation. This is a critical step. If you push the shell to far into the die the case length grows. You want to keep it shorter than .89. The case size of a Namu is .865. Otherwise, it becomes too long and you should trim it down before doing the final sizing in the Nambu die. Being too long will cause there to be too much neck and the shoulder will buckle or wrinkle. So don't push it in too far. If you don't push it into the 30-30 die far enough you will get a band around the base when you do the final sizing. So you may have to play with this distance depending on your Nambu die. You want the shell to go in far enough that the base is .412 in diameter... This is the size of original Nambu brass. I've seen documentation the base is .408. But cases I have measured came out .412. Could be my set of calipers, so you will need something in this range.

30-30 sized and regular 357 on the right.

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Reformed case fits 8mm Nambu shell holder.

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Normally the 357sig case will not fit.

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This shell is "right on" coming out of the 30-30 die. So I would do another 50-100 or ? just like it. Then it is time to move on to the final sizing in the Nambu die. Take out the de-capping rod. It is not needed and just causes problems. Quite often after the going through the 30-30 sizing die it doesn't take too much to form the final step. If it resists too much there is something wrong. Back it out. Check your shell size/length. Continuing to force it may cause the shoulder to wrinkle or give way completely. Normally you get the shell holder to just touch the die. If the shell is too long, this is where you run into trouble. Sometimes the shell just needs a little more lube. You should NOT have to jump on the press's lever arm to get this formed. Also beware that you could end up with the case frozen I your die. You won't know this until you try and remove it and shear of the base rim. Leaving the case stuck up in your die. Be careful.

I've started it into the Nambu sizing die and there is a little more binding than I would like.

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The neck is forming. A little more lube and back in it goes.

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We are done forming the brass. Here are three I made for this post.

Just need sizing and then load them up.

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Ok, which is which? From left to right. 357sig, my reformed 357, a HDS 8mm Nambu case, the real deal. My formed case is too long. It needs to be trimmed to .845 (documentation says .86) which is the proper length of a Nambu case. Next I will show resizing the case and then reloading the final product. Over the next six months I'll follow up with the average times I have been able to reload these reformed cases before they split.

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Because the 30-30 sizing step is so critical. I thought I would show you the following. From left to right. 357sig, correct formed 357 and on the right one that has gone too far into the 30-30 die. Remember, you want the base and the bottom of the case to be.412. Don't go too far. Like I said, in my die that is about 3/8 of an inch. There should be some shoulder left. If you don't go in far enough there will be a band around the bottom of the base. You may have to play with this. But use calipers as you go. Then lock it in and do however many you are looking to load.

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Ok get out your calipers. The newly formed cases are too long. If you place one (unloaded) into the chamber of your Nambu you will see the slide will not close all the way. It needs to be sized down to about. .865. I have a case trimmer that has two bases, one for pistol and one for rifle. So with the pistol base set up, it is time to size down all the formed brass. Once you have them the proper length, you need to take off the rough edges. Then you are ready to load them up. Here again is a formed and sized case next to an actual piece of Nambu brass. You can see a little different shoulder and the base lip is also a little different. But it functions perfectly and ejects with no issues or stress on the pistol since we sized it down to match the Nambu.

Next is the finished round. I bell the mouth and seat the primers. Then with a 357sig powder through the die, I can set up my powder drop and seating die on my turret press and do the final two steps together. And tada... a Nambu 8mm round.

My new Lee Classic Cast single stage. For some odd reason. The sizing of the shell is now one smooth stroke. No binding and I don't use any added lube.

My sizer.

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Formed case on left, Nambu on right.

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Last edited by Zeliard on Thu Jun 29, 2017 11:09 pm, edited 1 time in total.
Proud alumni of Transylvanian Polygnostic University. "Know enough to be afraid."

"Vertroue in God en die Mauser".-Faith in God and the Mauser.

"Send lawyers, guns and money." -Warren Zevon

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Re: 357sig brass to 8mm Nambu

#2 Post by Zeliard » Thu Jun 29, 2017 11:09 pm

Originally posted by the authors as indicated.


NOTE: These posts in the 357sig brass to 8mm Nambu thread contain some good information & questions so I’m adding them here as a reply.


Burner

As for your temp reloading bench.
If you get a piece of 3/4" plywood and bolt it to the top of the workmate you can do major reforms on RIFLE brass all day long.
I have been using the same setup for 10 years and it only takes 2 minutes longer to assemble and take down for storage.


GIJeaux

Have you thought about sacrificing a .30-30 die and cutting it down to the length that would allow you to simply push the SIG case all of the way through? That way you could do away with knocking the brass back out and it would make it a lot quicker to convert you brass. Plus, it would make the brass more uniform since you would not be making adjustments everytime you went to make brass.
Just a thought.

1Blue

I did try it and sadly it didn't work. The mouth of the die does have a more generous gradation, than the 30-30. However the actual dia of the die is just too much of a jump to get the 357 started. My press wants to really deform the case in order to get it started. It ends up with a serious vertical wrinkle in the brass.

I've been looking for another used 30-30 die to cut down. Oddly I have not found a used cheap one at any of the local gun shows lately...

On another note. Firing my formed brass has been great! No splits! I've reloaded some cases three times now and they look great.

Rapidrob

When you cut down the die, make sure to chamber the new mouth of the die. Remember to add the thickness of the shell holder before you cut.

1Blue

Another thought I had was to counter drill down from the top of the die. To a diameter that the brass can pass through. So once it is sized, it passes into an area of the die with a larger diameter and as you size more shells they just begin to come out the top... Much like the Lee bullet sizing die...

RWS

Not trying to be a naysayer here but Nambu pistols, and the wartime models in particular, are not noted for maintaining consistent tolerances. A small caveat is in order relating to those varying tolerances.

The rim thickness of .40 S&W and .357 SIG cases is in the .050" range. The rim thickness of 8mm Nambu brass is closer to .030". This is enough difference so that SOME Nambu pistols will not allow the extractor to ride over the rim of converted .40 & .357 SIG cases.

If the only consequence was a feed jam then it wouldn't be much of a big deal, but over the past few years I have observed more than one Nambu's extractor break when attempting to feed converted brass cartridges.

I would suggest that before anyone goes down the conversion route they try an unconverted .40 or .357 SIG case and see if it slides freely under the extractor with a tiny bit of clearance. If it won't slide freely then the cost savings will go downhill quickly if you have to start buying vintage replacement extractors. Again, this caveat applies only to Nambu pistols that have extractors on the tight side. Many will work with the converted brass cases; however, some won't.

-Bob

1Blue

I would recommend not firing your Nambu with the original firing pin or extractor. The firing pins can be weak and it would be the pits to break it. Regarding the extractor, you can buy a new one from Don at the link below. You can then check the tolerances and open it up with a small metal file. It'll run with no issues then and you still have the original. I also recommend a new set of springs.

S.B.

A couple of things I learned while trying this: I use a RCBS rock chucker press and back off the full length 30/30 die and readjust sizing die to give you all the mechanical advantage you can get.Rmington .357 Sig brass will not fit into a RCBS shell holder after using the 30/30 to size the rim on Remington Sig brass mikes(DC) .0554 thick while some factory brass I bought mikes(dial caliper).042? Can't remember what OP's brass was?
Also, I tried the Lee bullet sizer but, the 30/30 fl worked best.

1Blue

I've used all sorts of 357sig brass. Even nickel. There is definitely some brass that is easier than others. I traded for brass on ammo brass trader and bought some on gunbroker. If you loose the taper on your 357sig brass, you are pushing your brass too far into the 30-30 die. This will also squeeze down the base and it becomes too thick to fit into an 8mm shell holder for the final sizing in the Nambu die. Back off how far you are pushing your brass into the 30-30 die. It's fiddly work. But it does work. I make sure I have a shell spotter when I shoot this round. I want that casing back.
Proud alumni of Transylvanian Polygnostic University. "Know enough to be afraid."

"Vertroue in God en die Mauser".-Faith in God and the Mauser.

"Send lawyers, guns and money." -Warren Zevon

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Re: 357sig brass to 8mm Nambu

#3 Post by rickplayer » Mon Jul 10, 2017 9:29 pm

Does anyone turn the rim down? Make it thinner?

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