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Here you'll be able to follow along as I attempt to design and develop my own "wildcat" cartridge- the 35/40 Auto! 

The Goal! 

The premise of this cartridge is to duplicate .357 Remington Maximum performance with  125gr to 180gr bullets in a case that's shares the same C.O.L. as traditional 'magnum' revolver cartridges.  To futher it's utility, I hope to use 180gr and 200gr bullets seated to a longer length in semi-automatic carbines and lever-action rifles as well. 

To this end, (and for ease of conversion) I selected the 10mm Magnum case from Starline as the basis of the design.  Using an RCBS 357sig sizing die,  the cases are necked down to the point where a normal 10mm case would end.  The result is a straight-walled bottlenecked case with a 1/4" neck  and a profile like the familiar 7.62x39.   With the somewhat larger case capacity and slower powders, I hope the avoid the excessively high pressures and erosion problems that have plauged the Remington design while maintaining  it's ballistic performance. 

The Gun! 

The test barrel is a custom made 10" bull barrel for my Thompson Encore frame made by Bullberry Barrel Works of Hurricane, UT.  Sample (inert) cartridges were sent for fitting and it required about two months to finally receive the finished barrel and foregrip.  It was ordered tapped for a handgun scope, and so a Tasco 'World Class' 1.25-4x was mounted and bore sighted for me by Cliff's Gunsmithing, of Santa Ana, CA. 

The Ammo! 

Initial test loads were developed using information gleaned from similar cartridge designs and loadings found in the excellent "Cartridges of the World" 8th Edition by Frank C. Barnes. 

Pressure limits were estimated by the traditional primer/brass visual inspection method and loads were 'worked up' in the usual fashion.  Bullets velocities were determined with a Shooting Chrony Master Gamma chronograph placed 6ft. from the bench.  All measured groups were of 5 shots each on paper targets at a distance of 50 yards.  (Many thanks to the Inland Fish &Game outdoor range, for being so close to home!)