Found this whilst doing some web searches today. Sounds similar in concept to some of these other .06-based rounds. Anyone know anything about this cartridge?
Extracted from Cartridges of the World, 6th Edition, 1989.The 375/38-40 Rimless. The 357/38-40 rimless was developed as a cartridge for use in conversions of the US M1 carbine. It is, in effect, a rimless 38-40 winchester. It originated sometime in the 1960's by George Heubnar. There is also a very similar wildcat known as the .357 Shannon. Both cartridges are made by shortening and necking down .30-06 brass, and both have practically the same ballistics.
The M-1 carbine has been the object of a number of caliber conversions aimed at improving its usefulness as a hunting rifle for either varmint or big game. The 30 Carbine cartridge in itself is not a particularly a good varmint cartridge and is under-powered on deer sized animals. The 357/38-40 is an effort to turn the handy M-1 carbine into a legal deer rifle, something it does fairly well. The Cartridge is adequate for deer or black bear at short ranges. It would probably do almost as well as th 44 magnum fired in a rifle. Case capacity is slightly less than the 38-40.
180 grain behind 22 grains of 2400 with a MV of 1855 fps. (ME: 1380)
200 grain behind 20 grains of 2400 with a MV of 1800 fps. (ME: 1510)