No, you clearly don't understand our current gun laws.
I own a model 19 with a 4" barrel. It is restricted, because it is measures just over the 106mm length. A gunsmith measures this and sends in the appropriate paperwork, and it becomes legally re-registered as a restricted firearm.
This is the 3rd of such guns I have owned, and several have been in the EE recently. They aren't all that rare.
S&W 4" barrels actually vary somewhat in length, and if the 4" model you have measures out to be just over the line, it can be re-registered correctly as a restricted, not a prohibed firearm. Many such guns have been re-registered saving them from the prohib void.
If found in your possession, so long as you are the correct owner and registered to you, you are perfectly legal and will not be charged with anything. It is not a prohibited firearm if the barrel is legal, and is not otherwise listed as being prohibited.