problem with reformed .308 to 8 Kurz cases

[shortfal]

I have plenty of FNM and PPU cases for my Sturmgewehr shooting but made a good number from .308 just to see how they would work out.
I find that after firing a time or two the converted cases get a tight spot after sizing where the neck and shoulder join such that I have to ream again. Does that make any sense?
It does not happen with the factory FNM or PPU cases. I'd not think the heavier walls of the .308's would flow forward especially since the thinner factory brass does not. My loads are not hot at all. It's my first case forming venture so was wondering if any of you more experienced formers out there might comment. TIA
Pete in St. Louis

[bruce drake]

That constriction is called a doughnut and a common occurrence in reforming cases. Hit the Google search and you'll be able to find more information on it. I have the same issue when I reform 308 Win cases to 6.5 Creedmoor.

[Artful]

Yep, same as I found when forming 243

[AggieEE]

The doughnut was covered in an issue of precision shooting sometime in the 80's. Basically, if you neck turn at the desired cal. you leave metal on the shoulder that gets pushed into the neck at the base of the neck. Stop at one size above the cal. neck turn then finish forming. The bigger neck moves the ring further down on the shoulder and no more rings. BTW I'm jealous, is the Sturmgewer a early model or late? I thought the early model looked pretty neat with the sweep pistol grip. Might be a pain to shoot though.

[shortfal]

You are thinking of the FG42 of which there were early models with the severely angled grip and the later ones with a grip that was much less angled.
They shoot the 8MM Mauser round. The MP44's shoot a shortened (33MM case) 8MM round.
Pete

[shortfal]

The doughnut was covered in an issue of precision shooting sometime in the 80's. Basically, if you neck turn at the desired cal. you leave metal on the shoulder that gets pushed into the neck at the base of the neck. Stop at one size above the cal. neck turn then finish forming. The bigger neck moves the ring further down on the shoulder and no more rings. BTW I'm jealous, is the Sturmgewer a early model or late? I thought the early model looked pretty neat with the sweep pistol grip. Might be a pain to shoot though.

I'm not neck turning, I'm reaming the inside. Neck turning would be a real pain when doing 200 or more cases. Wondering if after shooting a couple times and reaming they might settle down to where the problem would go away.
Pete

[HangFireW8]

You have an MP44- that's cool!

Precision Shooting magazine called it the "Deadly Donut of Death", I don't know if it ever killed anybody, but I think it did ruin some benchrest rifles. I didn't get the magazine in the 80's, but the DDD was still a lively topic in the 90's.

The problem with reaming is the brass is elastic, and moves away from the reamer more at the shoulder than the middle of the neck. For the most consistent neck diameter, turning while the entire neck is supported by a mandrel is the way to go. However for your purposes it probably doesn't matter.

Reaming it after it appears will work. AggieEE's technique will help you avoid it in the first place.

[357Mag]

Shortfal -

Howdy !

For less total brass involvement and brass movement during case forming, you could form your 8mm's from 6BR or 7BR brass.
They are only about .22" longer than the " Kurze". Perhaps this would take the process more towards a simpler case oal trim; at the end of case forming ?

I made my .357AutoMag cases this way... making them out of both 6mmBR and 7mmBR brass.
Going to a neck-up from 6 mm or 7mm to the 8mm final diam you want, would serve mostly to " thin" and not thicken the necks.
Relocation of the shoulder on the BR case would not (IMHO ) likely cause the necks to seriously thicken.

Again.... for .357AutoMag cases, BR brass worked great !


With regards,
357Mag

[Bird]

Shortfal,
Your cases will not settle down, and the donuts will keep reappearing, thus requiring more reaming. I never ream, but always neck turn on a mandrel. Turning the outside of the neck will keep the donut at bay a lot longer than reaming, maybe even for the life of the case, and will give you better neck thickness control. The trick with outside turning, is to cut/turn slightly into the shoulder area of the case where the donut forms. Also minimal sizing of the case, and only bumping back the shoulder a small amount helps. The expanding button on the decap rod does not help the problem either. Get a custom outside neck die or make one from your existing sizing die.
For cartridge cases where the bullet base does not go below the neck/shouder junction, donuts are not as important, if you size as above.. I think that is not possible to do with the Kurz.

[shortfal]

Shortfal -

Howdy !

For less total brass involvement and brass movement during case forming, you could form your 8mm's from 6BR or 7BR brass.
They are only about .22" longer than the " Kurze". Perhaps this would take the process more towards a simpler case oal trim; at the end of case forming ?

I made my .357AutoMag cases this way... making them out of both 6mmBR and 7mmBR brass.
Going to a neck-up from 6 mm or 7mm to the 8mm final diam you want, would serve mostly to " thin" and not thicken the necks.
Relocation of the shoulder on the BR case would not (IMHO ) likely cause the necks to seriously thicken.

Again.... for .357AutoMag cases, BR brass worked great !


With regards,
357Mag
That'd be OK but the .308 cases are free and I have thousands of them. I'd bet those BR cases are pricey.
Thanks Pete

[shortfal]

You have an MP44- that's cool!

Precision Shooting magazine called it the "Deadly Donut of Death", I don't know if it ever killed anybody, but I think it did ruin some benchrest rifles. I didn't get the magazine in the 80's, but the DDD was still a lively topic in the 90's.

The problem with reaming is the brass is elastic, and moves away from the reamer more at the shoulder than the middle of the neck. For the most consistent neck diameter, turning while the entire neck is supported by a mandrel is the way to go. However for your purposes it probably doesn't matter.

Reaming it after it appears will work. AggieEE's technique will help you avoid it in the first place.

Good point re the cases being elastic. When I first formed them the reaming was done while the cases were still in the die thus being supported. The doughnut only shows up after the first or second firing/sizing. Reaming afterwards does not completely remove the doughnut as it's not done in the die. Could be the reamer has to be dead sharp so as to cut without trying to push through rather than cutting cleanly.
Thinking if the case bodies were inside reamed to below the neck/ shoulder junction before necking they would behave like a factory case that is not thicker right below the neck/shoulder like my reworked cases are. But, another setup, another reamer along with a special die to hold the case for pre forming reaming when factory cases are not particularly expensive might not make a lot of sense. Always fun to play with stuff though.
Thanks Pete

[shortfal]

Shortfal,
Your cases will not settle down, and the donuts will keep reappearing, thus requiring more reaming. I never ream, but always neck turn on a mandrel. Turning the outside of the neck will keep the donut at bay a lot longer than reaming, maybe even for the life of the case, and will give you better neck thickness control. The trick with outside turning, is to cut/turn slightly into the shoulder area of the case where the donut forms. Also minimal sizing of the case, and only bumping back the shoulder a small amount helps. The expanding button on the decap rod does not help the problem either. Get a custom outside neck die or make one from your existing sizing die.
For cartridge cases where the bullet base does not go below the neck/shouder junction, donuts are not as important, if you size as above.. I think that is not possible to do with the Kurz.

Good thoughts but these rifles are machine guns with chambers that can be somewhat large. All cases need full length resize. The boolit base does go below the neck/shoulder junction.
Interesting that the cases (factory or reworked) hold up well, most always tolerating 8 or 10 reloads or more. Losses are most always neck splits and not too many of those at all.
Pete

[357Mag]

Shortfall -

Howdy, again !

Thinking out-loud.....

Whack the .308's short to start with... a little longer case oal than final Kurze length.

2nd, run them through a .38-40WCF die ( LEE " seater die body " SB2795, or.... a " sizer die " from their .38-40 steel pistol die set.
( Reddding makes a .38-40 " form & trim die # 91366, and a " trim die " # 83366 ).

.38-40 has a nominal .455" diam shoulder, while the Kurze runs .444" ( data I've seen ).
The Kurze has a 19* shoulder angle, while .38-40 runs a mild 6* ( easier to neck-down cut-off .308 cases with ).
At 1.305"lg, .38-40 is only a scant bit longer on case oal than the Kurze.

After that initial neck-down to .40 calibre as detailed above, you then run cases through the Kurze die.

If the LEE die can work, that would only run $19 + shipping.

Worst case, you'd end-up w/ an inside neck ream... if the Kurze' necks formed too thick.


With regards,
357Mag

[shortfal]

Shortfall -

Howdy, again !

Thinking out-loud.....

Whack the .308's short to start with... a little longer case oal than final Kurze length.

2nd, run them through a .38-40WCF die ( LEE " seater die body " SB2795, or.... a " sizer die " from their .38-40 steel pistol die set.
( Reddding makes a .38-40 " form & trim die # 91366, and a " trim die " # 83366 ).

.38-40 has a nominal .455" diam shoulder, while the Kurze runs .444" ( data I've seen ).
The Kurze has a 19* shoulder angle, while .38-40 runs a mild 6* ( easier to neck-down cut-off .308 cases with ).
At 1.305"lg, .38-40 is only a scant bit longer on case oal than the Kurze.

After that initial neck-down to .40 calibre as detailed above, you then run cases through the Kurze die.

If the LEE die can work, that would only run $19 + shipping.

Worst case, you'd end-up w/ an inside neck ream... if the Kurze' necks formed too thick.


With regards,
357Mag
357, thanks for those thoughts, but I'm not having any problem forming. I cut the cases, lube and run into a standard Hornady or RCBS 8 Kurz die. Using an old Lachmiller press with a piece of pipe on the handle they resize just fine. The necks end up quite thick so I had a reamer ground with a pilot so the necks are cut to .012 thick while still in the die. The press is mounted on an adapter I made for the Bridgeport mill. That way I can line it up with the spindle and ream on that machine.
Pete

[runfiverun]

I'd grind a couple of cases open and measure stuff.
then you can see where the brass is coming from and why you'd need to re-cut the donut.
if you have a mill/lathe you could thin the case at that spot before forming and avoid all the trouble.

annealing every 4-5 go rounds might allow you some longer case life too.

[shortfal]

I'd grind a couple of cases open and measure stuff.
then you can see where the brass is coming from and why you'd need to re-cut the donut.
if you have a mill/lathe you could thin the case at that spot before forming and avoid all the trouble.

annealing every 4-5 go rounds might allow you some longer case life too.

I have sawed cases lengthwise that have been formed/reamed. As one might expect the transition in thickness from the .012 thick reamed neck to the shoulder is great. Thinning the case body before forming would probably be the way to go. If I ever make any more I might tool up to do that. A cut down .308 sizer to hold the case and a purpose ground reamer all setup in the Bridgeport would work.
Annealing would make sense but so far case life is good. I don't keep good track but I know I have loaded some at least 6 or 8 times only loosing one once in a while to a neck split.
Was thinking about a induction heating rig for annealing.
Pete

[runfiverun]

those are flippin awesome and fast too.
I thought about one to anneal cases for swaging, and just to do case necks, but chickened out and went with the torch method.

[shortfal]

those are flippin awesome and fast too.
I thought about one to anneal cases for swaging, and just to do case necks, but chickened out and went with the torch method.
I've seen video somewhere, maybe here, with guys using induction heating for case work. Probably the best way to go other than the cost of one of those units. There's plans for building but then maybe that becomes the thing rather than case forming.
Pete

[shortfal]

Maybe it is becoming the "thing". I just built one of the annealing machines from the thread on the AR15.com site that a post here led me.
I came across induction heating units on the net. 2 For $50 something. One is 1000watt and might have enough power for annealing my Kurz cases. The second one of the 2fer deal is less power but probably interesting to play with. Should get in a week or so. Then I'll see!
Pete

[EDG]

If the thickness is causing the rounds to not chamber it is a problem.

I shoot a lot of 7.65 Mauser cases with donuts and they don't hurt a thing because the chamber is still way larger than the loaded rounds.

[shortfal]

I just worked with some of the .308 to 8Kurz cases today. It has turned out that I have to ream them every time I resize them after firing to cut out that doughnut. If I do not it takes much more effort to seat the new bullets than it would in a factory FNM or Privi case. They go in hard enough that the case is likely sizing the lead bullets somewhat. So I start out with a bullet sized .324 and after going into the case it might end up .322 or .323. That cannot be good for accuracy and perhaps raises the pressure. I've never read anything about how how excessive bullet pull relates to pressure other than when case necks pinch in a undersize chamber neck area..
No problem for me with the chamber pinching the neck as these rifles have plenty large chambers.
Pete

[EDG]

>>>No problem for me with the chamber pinching the neck as these rifles have plenty large chambers.<<<

You can buy a set of .251 to .500 gauge pins and check the case mouth diameter after sizing.
For sure mashing up the base of a bullet is not good for accuracy.

[shortfal]

>>>No problem for me with the chamber pinching the neck as these rifles have plenty large chambers.<<<

You can buy a set of .251 to .500 gauge pins and check the case mouth diameter after sizing.
For sure mashing up the base of a bullet is not good for accuracy.
Yes. I have pin gauges from .063 to .625. The cases I reamed yesterday accept a .323 gauge. I just loaded some today and the bullets seated with what I'd consider acceptable effort. I'm interested to see what the primers look like after firing. I've loaded the Kurz rounds for the past 4 or so years and most always get primers (CCI#34's)looking flatter than I'd expect. Interesting in that considering the smaller internal volume of the converted cases I load the IMR 4227 well below the starting loads shown in the Hornady manual. Using the starting loads in the manual with factory cases and Hornady jacketed bullets the primers also end up flatter than one might expect. It's all a learning experience I guess.
Pete

[EDG]

If the bullets are hard to seat just expand the case neck some more.
in my BPCR single shot rifles I use an expander the same size as the bullet so I get only a little neck grip from the spring back of the brass.
For an MP 44 you might want more grip to insure trouble free feeding.


Yes. I have pin gauges from .063 to .625. The cases I reamed yesterday accept a .323 gauge. I just loaded some today and the bullets seated with what I'd consider acceptable effort. I'm interested to see what the primers look like after firing. I've loaded the Kurz rounds for the past 4 or so years and most always get primers (CCI#34's)looking flatter than I'd expect. Interesting in that considering the smaller internal volume of the converted cases I load the IMR 4227 well below the starting loads shown in the Hornady manual. Using the starting loads in the manual with factory cases and Hornady jacketed bullets the primers also end up flatter than one might expect. It's all a learning experience I guess.
Pete

[shortfal]

If the bullets are hard to seat just expand the case neck some more.
in my BPCR single shot rifles I use an expander the same size as the bullet so I get only a little neck grip from the spring back of the brass.
For an MP 44 you might want more grip to insure trouble free feeding.

A somewhat larger expander might work if I annealed the necks/shoulder area but as is I'm thinking that the neck/shoulder area where the doughnut is might spring back in some and the neck stay opened up since the shoulder is somewhat thicker brass than the neck . They were never annealed after the conversion from .308. I about have my annealing machine done, then I can try the annealing. Otherwise I'm stuck reaming most every time I resize them. I have a setup I use in my Bridgeport for reaming but it is still time consuming and I'd just as soon not have to.
I do need a strong bullet pull for feeding but like I said I'm concerned too much might be swaging my lead boolits down to where accuracy is affected. These are not target rifles but can shoot better than some guys might think.
Pete
Pete