Nambu split cases

[brettkeating]

This started as a question in the Curio section, because the Nambu T-14 I have wasn't properly cycling some ammo I bought online, and thought it might be the gun. After spending time narrowing down the problem, I believed it was that the ammo was underpowered. Ends up it's more of a reloading problem now, so I'm moving that part of the discussion over here.

Finally got a chance to try out my experiment to see if underpowered ammo was indeed the problem. The conclusion seems to be that it is. But the results are a bit disheartening, in that any proper charge seems to split these reformed 40 S&W cases.

The pistol powder that I had available was 700X. I pulled 48 of the rounds that I had which wouldn't cycle... These were 85gr bullets in reformed 40S&W cases from Buffalo Arms. I reloaded them with 3.0 - 3.5 grains (8 each at 0.1 grain increments), and the 100gr plated bullets from Huntingtons. I got those loads by combining a couple internet sources. The ammo I pulled is advertised as "one-fired reformed 40S&W cases."

3.0 and 3.1 wouldn't cycle the action after the first round. 3.2 got hung up after about 3-4 rounds (similar performance to the ammo I already had). 3.3 and 3.4 cycled the action fine for the entire 8-round magazine. 3.5 started blowing the magazine loose, although the action did cycle.

I thought I was successful at 3.3-3.4, until...

Unfortunately, after collecting the brass, I noticed that a couple of the 3.3 rounds had split cases, and more of the 3.4 rounds did as well.

The OAL was 1.223", which is close to the OAL of the original ammo.

I'm not really sure how to proceed with this. It seems like if I get enough pressure to cycle the action, I end up splitting the case. I don't know if using a different powder would help here. I am thinking of retrying the experiment, but lengthening the OAL a bit (by about 0.025") to see if that makes any difference... I may also try getting my hands on some new correctly-stamped brass, in case the reforming from 40S&W is weakening the brass too much.

I've seen threads in other forums where others have had similar problems, where reformed cases don't make it past the first firing.

Any other ideas? Outside of annealing the cases? If I use reformed brass am I just going to have to treat it as expendable?

[mark501w]

I don't know about reforming cases for your pistol but, it sounds like .40 cases are under sized. You need a close fit For safety . Why don't you buy the proper cases? Try Cerro Safe to check chamber dimensions. You may have a war time variation on your chamber.

[brettkeating]

I'd like to but they aren't generally available. I would like to do that

[mark501w]

.357 sig cases?

[brettkeating]

357 sig sounds like it's worth a try. I found another thread online where a guy was able to get 3+ reloads in reformed 357 sig, using a similar forming process as used for 40 S&W. Unfortunately 357 sig is nowhere near as common, but if it holds up for more reloads, might be worth just buying some fresh brass.

[glassparman]

The 40 S&W cases start out larger than the nambu cases. I have some original to compare with. I have heard a lot about the 40s splitting but not sure why.

I myself just found some .357 sig cases so I'm going to give it a try . . . Just as soon as I can find the Nambu dies at price I can afford!

I have read that the trick to doing a case mod like this is not trying to size it all at once. As for using the .357 sig, I read that sizing it into a .30-30 die with the decap/expand rod removed, will get the case just about right for the Nambu dies. Keep this thread going and let us know how it goes.

[sunborder]

Just an odd thought, but have you considered annealing the case mouths? This is commonly done with rifle brass to prevent case mouth splits. Are the cases splitting at the mouth, or somewhere along the length/base of the case?

[3RDGEARGRNDRR]

Not an odd thought. This sounds like a must. That and maybe powder selection change. Or look over the firearm for the cycling issues.
Have you shot nambu cartridges to ensure its cycling? Also to mic out your reloads and compare to the milsurp stuff

[brettkeating]

Sorry to have let this thread die. I haven't returned to Nambu reloading in awhile, but may start working at it soon. I have enough to keep me busy lately with other things

I have not considered annealing the case mouths, but the splits were actually more at the shoulder.

Also, I can't find original Nambu ammo to make any comparisons, unfortunately.

One thing that is in process, however, is a backorder on properly headstamped unfired brass from Brownells. I have no idea if the order will ever be filled, but that's what I'm banking on for the moment.

[brettkeating]

I am also looking into getting 357 SIG cases. I will try with once-fired first, just to see how it goes. I have 30-30 dies and Nambu dies, so I should be GTG once I get them.

[Bornonthe4thofJuly]

^^^ Top Brass has once fired .357 Sig nickel plated case 60.00 per 1k.

[gblacksmith]

I am also looking into getting 357 SIG cases. I will try with once-fired first, just to see how it goes. I have 30-30 dies and Nambu dies, so I should be GTG once I get them.

I shoot 8mm Nambu and the cases have a fairly sharp shoulder, given their size. Just reforming the case would likely work-harden the neck & shoulder area enough to prompt splits.

I would try forming the case THEN annealing the neck/shoulder area.

I would try spinning the case in a drill, using a socket and square stud. Chuck this assembly into a cordless drill, light a propane torch. Commence spinning the case somewhat slowly.

Place the neck'shoulder area of a pre-polished spinning case in the outermost area of the flame until you see the heat rainbow start on the shoulder area. Immediately drop the case into a bowl of room temp water. You are now ammealed. Don't soften the body of the case, just the neck/shoulder area.

I have had great results with this method

[brettkeating]

I shoot 8mm Nambu and the cases have a fairly sharp shoulder, given their size. Just reforming the case would likely work-harden the neck & shoulder area enough to prompt splits.

I would try forming the case THEN annealing the neck/shoulder area.

I would try spinning the case in a drill, using a socket and square stud. Chuck this assembly into a cordless drill, light a propane torch. Commence spinning the case somewhat slowly.

Place the neck'shoulder area of a pre-polished spinning case in the outermost area of the flame until you see the heat rainbow start on the shoulder area. Immediately drop the case into a bowl of room temp water. You are now ammealed. Don't soften the body of the case, just the neck/shoulder area.

I have had great results with this method

Never tried annealing before so I have a couple questions. It doesn't look too difficult but I'm trying to quantify the effort and benefit. Approximately how long does it take for each case to heat up before dropping it in the water? Also, do you need to do this after every resize, or only once? How many more reloads do you end up getting out of your Nambu brass if you anneal?

Thanks!

[brettkeating]

^^^ Top Brass has once fired .357 Sig nickel plated case 60.00 per 1k.

Yep I think I may have found a 1k batch for $40, so that seems worth a try for sure