How to make a custom case sizes?

[BAC]

Hello all!

In designing a cartridge recently based on some specs outlined in an interesting conversation, it occurs to me that no round with a .408 diameter case head exists. The closest thing to it is the .410 case head of the 6mm SAW, which of course would be rare as hen's teeth or honest politicians.

That said, what would be required to make a custom-sized brass case? If it requires an extensive and specialized skill set, does anyone have an idea in mind of what it would cost to have them made? I'm hoping it won't be too prohibitive, but I have no frame of reference to even estimate a cost from.

 

[CJ6]

Well if you have a lathe and some brass rod stock or brass tubeing you could make your own. The Handloaders Manual of Cartridge Conversions by J.Donnelly & B.Towsley has some info on it. A great read and resource book.

 

[lelongcarabine]

What case geometry are you trying for; dimensions? A .225 Winchester could be swaged down at the head, to your specs. It is about .423". The dies would be pretty expensive, I imagine ! However, not as expensive as doing a minimum, special order of cases from Lapua, for instance ;D

 

[BAC]

CJ, thanks, I'll check out that book for sure.

Lelongcarabine, I figured any special order would be expensive, but the question is how expensive. If it's in the thousands of dollars range then yeah, I'll find a way to make it on my own. ;D

Exact specs I'm still trying to flesh out. I wrote a bit about it on another site (here). The only information I started with was this:

• Caliber: 6mm/.243"
• Case head/rim width: 0.408"
• Shoulder diameter: 0.391"
• Max case length: 1.642"
• Max overall length: 2.260"
  
• 93 grain bullet at 2850 fps from a 20" barrel at @ 52,000 PSI

Not knowing what software the individual used to calculate this, I'm freehanding it for the moment until I can pick up some ballistic software and information on bullet dimensions. Bear in mind that I'm very much an amateur to all of this. Below is what I'm currently at (bold indicates known values, italics indicate unknowns fleshing out for the sake of getting numbers on paper):

Diameter of bullet – 0.243
Width at top – 0.272
Width at bottom of neck – 0.272
Width at top of body – 0.391
Width at bottom of body – 0.407
Width of groove – .350
Width of rim – 0.408
Maximum case length – 1.642
Height to top of shoulder – 1.470
Height to top of body – 1.420
Height to top of groove – 0.150
Height to top of groove stem – 0.100
Height to top of rim – 0.060

Max. overall length (inches): 2.260

 

[fusionrider]

the suggestion of the 6mmAR on the sniper forum appears to be the answer to your question.

but if you want a project... Most every combination of case bullet and powder capacity has already been tried and you would be wise to read the conversion manual ,it is a wonderful resource, then decide what you want to do differently and modify existing brass. Inventing new head sizes is the work of well funded corporations and the Independently wealthy. good luck

 

[BAC]

the suggestion of the 6mmAR on the sniper forum appears to be the answer to your question.

Well that was easy.

but if you want a project... Most every combination of case bullet and powder capacity has already been tried and you would be wise to read the conversion manual ,it is a wonderful resource, then decide what you want to do differently and modify existing brass. Inventing new head sizes is the work of well funded corporations and the Independently wealthy. good luck

Well, as I don't head a well-funded corporation and am not independently wealthy, looks like I'll have to put that idea off to the side for now.

I appreciate the candid response.

 

[FilippoMo]

You should really consider 6.8 SPC as a parent case
which is very close to what you are looking for.I think that .012 oversize is something you could live with.
Sincerely
Filippo

 

[butchlambert]

Case Forming dies are not that expensive. Check these out on www.shadetreeea.com
Butch

 

[BAC]

Thanks for the suggestion Butch. Does that die set actually allow me to narrow the case head or just body length/taper/etc.?

You should really consider 6.8 SPC as a parent case
which is very close to what you are looking for.I think that .012 oversize is something you could live with.
Sincerely
Filippo

This idea has me very, very interested. Necking down a 6.8 SPC will give me the option of using 6.8 bolts and magazines (definite bonus). It even looks like a couple folks are already playing with the idea of 6mm bullets out of 6.8 cases. I imagine the longer case might limit the bullets, so shortening it a few mm and sharpening the shoulder angle might let me keep enough neck to securely hold 100gr (maybe longer) bullets without sacrificing too much case capacity.

Has anyone here tried necking down 6.8 SPC to 6mm? Or even o) 6.5mm?

 

[butchlambert]

Our dies will allow you to neck down to 14 cal and to as short as 3/4" total case length. Of course you can do anything in between.
Butch