The reason I'm asking is that I want a .40, but found a used .357 at a local gun shop that is absolutely mint. The guy at the gun shop told me I wouldn't be able to swap in a .40cal barrel, he said you can only swap down in caliber, not up. I'm just trying to understand why that is if you're changing the barrel?
And if a 9mm can be swapped with a .40cal (which is bigger), why can't a .357 accommodate a .40 cal barrel? Or is it something that I just have to accept as not being available?