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Dimensions of 7mm Sundra cases, loads, and effectiveness. Thanks for the help.

dfcjr,

google is your friend:

http://www.reloadersnest.com/frontpage.asp?CaliberID=335

I understand making brass is a PITA, but I haven't tried it...

jim

I like and use several wildcat cartridges but If I was going to build a fancy 7mm, I would go 7STW or RUM. Hard to beat those two.

Jim,

What is the parent case for the 7mm JRS?

TIA,

Don

Don,

IIRC, the parent case of the 7mm JRS is the 9.3x62 at least originally. Seems like there was an article in Handloader or Rifle magazine about it. HTH...

Grasshopper

The 7mm JRS is a wildcat from John R. Sundra, a writer for Guns & Ammo. It is a version of the .280 Remington Improved that gives near 7mm Rem Mag performance. The design uses the usual minimum body taper but gains maximum case capacity by pushing the shoulders forward. The 7mm JRS dispenses with the typical wildcat 40 degree shoulder for better case life and magazine feeding.

This text is based on information from �Cartridges of the World�, Hodgdon reloading manual, the cartridge designer and/or own resources.

I guess it would be similar to the Gibbs but with a shallower shoulder angle. I believe that brass forming would involve necking up to a larger caliber then necking part of the neck back down to size to form a false shoulder for the cartridge to headspace on during fireforming.
If it were me, I would go with a 280 Ackley or the Gibbs in that order. Just depends on whether you anticipate ever needing to sell the rifle. The Gibbs would probably be harder to sell and bring less money. The 7mm Sundra would be even more so I would think.
But if the Sundra trips your trigger, go for it. Sounds like fun!

To form the JRS you need to neck up to 30 cal and size back down to form the false shoulder until the bolt will just barely close on the loaded case and they will form just like any other IMP case when fired.