I'm guessing that the barrel & bushing may be all that is required but I'm not sure about the recoil spring. You may have to play around with some different weights to make it work right. It is an interesting idea, but the 10mm is plenty hot for car/truck door penetration.
I dont know about the feed ramp and case length, could be some problems there.
Why convert "downward"? The .357 SIG is a lesser cartridge, not a greater cartridge than a 10MM. The shop I work at developed the first prototype of the cartridge. We developed it for IPSC use, and someone obviously saw a potential - they sold SIG on it! It fits in 9MM length double stack guns - and it helps promote SIG-Sauer, basically. Powder space and bullet frontal area are both greater on the 10MM, and velocity is almost the same. Is the .357 SIG a good round - yes, but it's not up to a 10MM.
Kind of the good big man vs. the good little man argument. The 10MM is the most efficient, versatile and powerful handgun "Service" round ever made. But if you want to play with it - why not? The Delta can be a 10MM, a .40 Short and Weak, a .357 Sig or - if you really want 9MM performance - a 9x25 Dillon (10MM necked to 9MM). (Over 1700fps!) Works great w/a compensator. Enjoy.
Warmly, Col. Colt
"Beware of Counterfeits and Patent Infringements"
[This message has been edited by Col. Colt (edited 05-31-2001).]
I've fired just such an animal and found that it was more controlable than a full-power 10. It was fun to shoot and I had a big grin on my face after one mag. That's reason enough to have one. I think Barsto makes the barrels.