Maybe so, but five .40 cal holes will not physically fit into a "J" frame cylinder; just not big enough around.
There's also the matter of fitting a .40 cal hole into the J frame barrel and not having any metal left in the threads.
Even a "K" frame could use a little more metal in the barrel threads in .40 cal.
At "L" frame size, a .40 cal hole meets all these criteria with enough metal for durability. It's called a 646, no longer in production.