Originally Posted by
buffybr
.38 Spl shells can be shot in .357 mag but they are still .38 Spls. Pressure is determined by the volume of space that is available for your powder to burn in. The initial high pressure spike occurs before the bullet leaves the case. Too hot a load in a smaller .38 Spl case could create a pressure spike greater than the strength that a .357 mag cylinder can hold.
.38 Spl shells make great low recoil shooting from .357 mag revolvers. If you want the power of a .357 mag, load .357 mag cases.
The space below the bullet is the key. Technically it is safe,
IF you follow .357 mag load data,
AND if you keep the overall length the same that the data specifies. This requires that the bullets crimp groove to be above the case mouth, which means the other five bullets could move when you fire the gun. The only safe way to load a .38 case to .357 mag levels is with a cast bullet that has an extra crimp groove to keep the cartridge at the length of a .357 mag.