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Thread: 8 Nambu resizing question

  1. #1
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    8 Nambu resizing question

    Hi,

    A friend has an 8mm Nambu that hasn't been shot 20 times since it was brought back from overseas. I found a set of dies for it and bought some factory brass, as well as formed some from 40 S&W and 357 Sig. They all seemed to shoot OK. I was going to reload the fired brass and the case just doesn't look right. Here are three cases, as bought (unfired?), fired by us, and partially sized (L to R with the pic right side up).

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    Sorry, the pic is upside down and I don't know how to rotate it.

    I am using a tool similar to a Sinclair Comparator to set the shoulder to the correct spot with the sizing die. I hope to push the shoulder back .005 or so from the fired case. That's where the problem comes in! The fired case looks like the case neck is pretty much gone. If the unfired case is set to .000 with the comparator, the fired case has the shoulder blown forward .054. The partially sized case has the shoulder forward .041 from unfired, but I pushed it back .013 from fired and created a little bit of a case neck. I don't really think it's enough of a neck to hold the bullet, but I also don't want to push the shoulder even farther back and risk case separations.

    Are my fired cases "normal" for the 8 Nambu round? Any suggestion for where to set the shoulder?

    Thanks!
    Last edited by garandsrus; 06-07-2020 at 10:10 PM.

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    Hi-- I've had a Nambu for about 35 years, but have never fired it. Were I to suddenly get the urge, I think I would start with some loaded ammo, fire it, and then just follow the instructions that come with the reloading dies about how to adjust them. Usually, to screw the sizing die into the press until it contacts the shell holder. In reading through your post (several times) I understand your desire to get a fit to your chamber as closely as possible to extend the life of the brass, but have you had separations? I can't see someone firing a Nambu thousands of times, or even hundreds really. They are known to break firing pins, especially if dry fired, so I'd be on the lookout for a spare or two.

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    Thanks for the reply. My main concern is that the shape of the fired brass from this pistol is so different than what the 8 Nambu case shape should be. Having the neck move forward .054 is a LOT. It may be normal for this round, I have no idea, which is why I asked. I have never seen a fired Nambu case other than the ones we fired.

    New brass is about 50 cents each so getting more than one firing from a case would be good!

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    You're welcome! For what it was worth.

    Chambers in individual weapons can vary in shape and size....... Brings to mind the experience I've had with .303 British rifle cases. I own several of these rifles, and have some that will produce sharply bottlenecked fired cases and some that will be rounded as is your pistol ammo. I've heard various theories such as the rounded ones were purposely made that way for better extraction under combat conditions, since they didn't reload the cases anyway, all the way to the chambering reamers were worn from wartime production.

    Fifty cents each is expensive, but I think I paid $3.10 each for .43 Spanish. I'm just shooting in the dark here (that's a good one!) not having any real experience with Nambus (as I explained), but think you'd be more likely to experience split case necks from excessive resizing rather than separations. But, I'd still go with just reloading them in the standard manner, and keep my eyes open for more brass at a better price. They have made Nambu brass from such cartridges as .38 Special, but you have to be a really devoted tinkerer to want to do it. That's how Mr. Potterfield got Midway USA off the ground, by providing 8mm Nambu brass, eventually sold out, and never followed up with more, years ago now.

    What model Nambu do you have-- large or small trigger guard? Mine is the earlier pre-war model with the small guard. Very well machined.

  5. #5
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    I spent $$$ and hours forming 40 cal brass into Nambu last year but can’t for the life of me get the rounds to feed.

    I gave up and bought cases from Graf’s a few months ago but haven’t loaded yet. Maybe try this weekend.

    Personally, I would full length size per instructions in die set and not worry about measuring headspace. Drive die down to shell holder and do a drop test in barrel. The time you waste on protecting your brass isn’t worth the money IMO. How much you really planning on shooting it anyway? Guessing it won’t be an often thing. If so, I apologize... just ignore me.

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    We do hope to shoot the Nambu more than a couple times per year, 2-300 rounds total, but probably for no good reason other than nostalgia. It will only be shot at steel targets that are relatively close. With the "feature" that you can press on the external portion of the sear and firing pin will drop and the gun shoot, it's not like he is going to ever use it for anything other than a range toy.

    I did reform brass from both 357 Sig and 40 S&W and both shot fine. I had to run the cases through a die to reduce the overall diameter to Nambu size. Forming the shoulder in the sizing die wasn't much different with either case. I do need to trim the cases though, after forming. I didn't expect to do need to do that, but I do.

    djryan13 - I think I had to trim some off the shell holder so that I could screw the die down enough to form the neck in the correct spot. If you do shoot some rounds, I would be interested in seeing a picture of the fired case.

  7. #7
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    GONRA has five 8 mm Nambus in my weighty reference collection.
    Have 8mm Nambu RCBS dies, lottsa factory brass (Midway, FC) / bullets (FMJ, cast) etc.
    but never get around to load it all up....

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    Quote Originally Posted by garandsrus View Post
    With the "feature" that you can press on the external portion of the sear and firing pin will drop and the gun shoot, it's not like he is going to ever use it for anything other than a range toy.
    Ahhhh......so then it would appear that you have a Type 94 rather than the more common Type 14 that I had envisioned. Disregard the remarks about the firing pin breakage.

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    The pistol belongs to a friend. Yes, it is a Type 94 based on comparing the pistol to pictures of the 14 and 94. I know very little about the Nambu. He has an original magazine with the wood circles (not sure what they are called) and a second magazine, which is the one we used. It was a bring back by a friend of his and then given/sold to him, but don't know any details of how the pistol was originally acquired. He has had the pistol for 20+ years and has a box of ammo made from 38 Special cases that gives a very strange look to the case after being shot. Apparently, some cases rupture, and some don't, which was OK to the ammo maker. I don't think he had fired it more than 3 or 4 times before last week.

    I told him that I would load some ammo for us to shoot but then I saw the price of reloading dies! I eventually found a reasonably priced set along with the brass I mentioned. I also have some 80 and 100gr bullets (approximate weight - I don't remember the actual). Reloading data is scarce but I did find some, including Larry Pottersfield's information.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
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LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check