Nope they're different. I wonder if it is a Navy , Air Force [Or AAF back then] thing. Navy planes have the primary outboard, F4u and F6f, while the 51 has primary inboard. I believe the P47 has its inboards as primary also but I don't have enough Jug time to remember [confirmed, P47's primary are inboard also].
There is a 'Select Primary' weapon like secondary but when I tried that , the results I got were sooooo waacky I never do it ingame.
fuzeman