Case shoulder bumping

M

Mirage416

New member
Case shoulders can be made longer by the process of fire-forming them in a longer chamber.

What can one do if a case shoulder is needed to be made shorter?

I am shortening the neck of a case by trimming it 0.130". After I trim the neck down, I would like to gain some of the neck that was lost by pushing the shoulder down and increasing the shoulder angle. I would like to move the neck/shoulder junction of the case down by roughly 0.060".

This is being done to meet a certain OAL length requirement of a new cartridge I am developing.

Does anyone have experience with working brass down like this in a die? I have bumped case necks down by smaller amounts myself with a bushing die, but I am unsure if what I want to do (changing the shoulder angle) is possible without improperly deforming the case while running it into a die.

Thanks
 
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You can push a shoulder back as far as the brass will allow. Some heavy thick brass is miserable to work with, but I've run a .30-06 case into a .243 Win FL die just to see what would happen. A REALLY strange looking .243 case with a VERY long neck. If the brass is too thin or too soft and you try to sharpen the shoulder much you can lose cases too. If you're planning on forming very many cases like this it can end up being a pain in the tail.

What case are you working with BTW?
 
I'd say that you need a F/L die that matches your parent case, then have .056" cut off the bottom of the die (for a nice .004" crush for headspacing like the Ackley Imp's). Then resize the case which will push the shoulder back, trim to desired OAL, neck turn (neck walls will thicken from the shoulders extra brass), then load in the new chamber and blow out the shoulder to match. I think if you try to push a 20* shoulder back with a die that has a 30* or 40* shoulder you may cause the case to collapse.

This is the way I would try first anyway.

Dave
 
I make 30 herret brass from 30-30 which involves shortening the shoulder almost a 1/4". I havent had any collapse-yet. It is a pain in the butt process.The shoulder angle is only changed slightly though. I never thought about measuring neck wall thickness. Maybe I should start.
 
I am taking the new Remington 30 AR case (which is not a 30 Remington BTW) and shortening it to 1.40" OAL.

The case comes standard at 1.53" OAL. Technically, I could just trim 0.13" off the neck and have a case that works for 1.40" OAL. The neck would just be a shorter neck.

I'm not sure what the trade off is exactly for having a short neck, but I have seen some cases with really short necks out there. Heck, I may be able just to simply trim the neck, and blow the shoulder forward for more capacity, instead of pushing it back to gain more neck. What do you think?

I am doing this because of an actual regulation on bottleneck cases we can use for pistol shooting. The case OAL must be <1.40" and .30 caliber minimum. So far, this looks like the perfect case to meet these regulations and put in a bolt pistol.

url
 
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Why not just do the same to a 30BR, Lapua brass is far better than Remmy brass.

What is the diameter at the web on the 30AR?
 
I found it, rebated .308 sized rim with .500" body. So it will have a little more capacity than a 30BR.

30 Dasher then!!!
 
Yeah, could it even be called a 30 Dasher since it is larger than a BR case? I was thinking of an all new name to designate the larger 0.500 body, and it's also a bit shorter. I don't know, it's not like I plan on the cartridge spreading and being used, it's just something to fit my needs.

I think the neck might be alright at the trimmed length, without pushing it back. There is 0.155" of neck contact to the bullet. So from here I believe I could just blow the shoulder forward, leaving the neck/shoulder junction where it is. It would be a very subtle case capacity change.

Here is one trimmed at 1.40"

30arshort.jpg
 
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If you don't want to cut a die off, you can face off the shell holder. The 'standard' shellholder thickness is .125, so with .060 off it's going to get a bit thin...might still work with a good lube on the case and no expander ball to drag back over. But a cheap f.l. die cut off is still your best bet. I've made hundreds and hundreds of shortened 308W's this way.

Make sure and post some pics of your finished case. -Al
 
Let me just say that my initial idea for this case, the lowering of the neck/shoulder junction, was simply my guess at how to properly finish the neck shortening. However, with my limited experience in this area, I'm not so sure I am on the right track. So I would like to ask those with more experience than me, what would you do here?

Would you leave the shortened 0.155" neck alone where it is, and blow the shoulder forward, or should I push the shoulder back the 0.060" or so, change the shoulder angle, and gain some of the neck back? I might sacrifice a couple of grains capacity to do the latter, but I don't need maximum speed. I really just want it better suited to accuracy. That is where I get confused, not knowing whether speed will help accuracy, or if a longer neck will.
 
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If this is going to be fired from a single shot pistol and the chamber will obviously be a custom you could likely just trim the cases to 1.40" and go for it. It might not be the best for absolute accuracy, but for hunting it'd likely be plenty accurate. Going to a whole bunch of pain and aggravation just to get a round that fits some silly hunting reg doesn't make a lot of sense to me, I'd do it the simple and easy way.

Yes I've been told I'm lazy, but it doesn't bother me because I am.
 
Larry,

There isn't much more pain and aggravation involved than asking some questions in the forum. Either way I still size brass. Either way I still fireform. Either way I still have a chamber cut. Doing it right is no harder than doing it wrong here.

This is a bench pistol with 20" heavy barrel and target action. It will no doubt be a very accurate rig close to a bench rifle that has no butt. I am concerned about doing the case right.

And Larry, this is it for cartridges capable of such a thing in a pistol, that meets the regulations. The BRs are longer and skinnier. There is but one other cartridge out there that meets regs, it is known as the 30 Bellm. Take a look at it. It only holds about 25 grains of powder, unfortunately. This new AR brass is great for the task at hand, with its capacity and short length.
 
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