Not much other than the diameter of the muzzle opening on the slide. You can buy after market barrels that are bigger in diameter to compensate for this to make a conversion from .40 to 9mm on most HK pistols.
Negative, the muzzle hole on the slide would be too small and an aftermarket barrel would have to be made dangerously thin and I doubt anyone is willing to do that, just not safe.Can you go from 9mm to .40?
No.Can you go from 9mm to .40?
This is true.... :wink:And the extractors are more flexible, too!