5.7 mm Johnson Spitfire

Around 1986, I bought an Iver Johnson carbine chambered for the 5.7 mm Johnson (a/k/a Spitfire) cartridge, which is a 30 M1 Carbine case necked down from .308 to .224.

I bought a set of custom dies from RCBS to form the cases and load them. RCBS does not provide load data for the cartridge and the only things I could find were in Cartridges of the World (i.e. 40 grain bullet and 12 grains Hercules 2400) and an old Pacific manual (i.e. 40 grain bullet starting at 12 grains of 2400 with a maximum of 13.3 grains) which was provided to me by the NRA along with a disclaimer that the loads were probably too hot. When loaded in accord with the Cartridges of the World data, the cartridges show flattened heads consistent with chamber pressures that are too high. Even dropping as low as 11 grains of 2400, the brass still showed signs of distress.

In accord with the instructions provided by RCBS, I do ream the necks of the newly formed cases to a thickness of 0.012.

If anyone can provide any assistance in either the selection of powder and bullet weight or the diagnosis of the procedures followed, I would be very grateful.

Thanks in advance.

Thanks

Thanks to everyone who posted.

I will definitely look at the links as soon as I get my head above water at work. I only have a chance to go to a rifle range that will let me keep the brass for subsequent analysis about once a quarter, so it may be a while before I can post results, but I will definitely post when I have them.

Sunray said:

Grafs wants $305.91 per 1,000. What you really need is a Redding case forming die from Midway. $84.99. Same thing from RCBS runs $99.99.
For anything that is remotely unusual(ain't nothing more odd than 5.7 Johnson. Except .41 AE.) always buy as much brass as you can afford. And forming dies.

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I already have the RCBS case form, case trim as well as 2-die reloading set. Are you suggesting that I should be using the Redding die instead? If so, can you explain your reason since it not apparent why I would it need it in addition to the RCBS dies.