I have a 455 Tacticool that I wanted to try a .17HMR varmint barrel on and it was on sale at CZ USA, so I bought one. It showed up today and I was all excited about swapping out the .22lr barrel and going to the range. One of the first lines in the directions says it must be fitted to the rifle by a gunsmith. I thought they were drop in kits. Do they REALLY need to be fitted or is this CZ making sure they cover themselves for liability reasons?