Sorry if this has been discussed before in here, but what are the differences between the interchangable P320 grips for the 9/357/40 and the .45? Supposedly they are not interchangeable, but has anyone actually tried it? Will the FCU not fit right in one or the other? Reason I ask is because I have a compact/small/fde grip for my 9MM, but I have only been able to find that combination in color and size in .45. May FCU fits and functions fine in it. Maybe you can fit a 9 in the 45, but not the other way around. Thoughts/observations?