The .240 Howell is based on a custom lengthened .30-06 case with 0.375-inch neck and 25� shoulder. I don't have any load data and wouldn't publish 'em if I had 'em. QuickLOAD software is the best way to get a good preliminary idea of its performance.
The twelve cartridges in that line are designed for improved performance with heavy premium bullets at moderate pressures. The .240 Howell is a bit "hotter" than a 6mm-06. It can be formed from .30-06 cases but with a very short neck.
Head-stamped .XXX Howell cases are available for several of the line, but as far as I know, .240 Howell cases have not been made. They can be formed from the Howell Basic cases available from Huntington Die Specialties in Oroville, CA, (
http://www.huntingtons.com) and American Hunting Rifles (
http://hunting-rifles.com).
You can get some (visual) idea of how the .240 Howell compares with the 6mm-06 from comparison photos of other Howell cartidges at
http://hunting-rifles.com/Ammo/case_compar.htm. Except for the shorter .220 Howell, all the other cases in that line are the same length.
