FN 6x51

I got this case today in a box full of various cases:

Headstamp is “(+) FN 63”. OAL is 51mm, inside neck diameter is approx 6mm. There looks to be marks on the neck from necking down. Apart from the neck being a bit short that case is identical to a .243 Win. Was this just someone forming 7.62x51 Cases into .243 for shooting or could this be some sort of experimental round (unlikely)? This is a fired case, but is Berdan primed, so someone either got these as NPE brass or pulled the 7.62 NATO bullets from them to resize them as .243 rounds.

Labbett (Assault Rifle Ammunition - 5.56mm to 11mm calibre) describes an FN experimental 6.5 x51mm cartridge for the Swedish Army - hs is given as (+) FN 62. The bullet diameter is given as 6.8mm. This compares to 6.18mm for the 243. A photo of the 6.5x51 is shown in Jean Huon’s book on Military Rifle and Machine Gun Cartridges. Unfortunately, I have been unable to find exact measurements of the cartridge or whether (+) FN 63 cases exist.

Dave S

Yes, FN even made up some FAL in 6.5x51mm for the Swedes to test. Rarer yet is the prototype FAL in 6.5x55mm made for previous Swedish testing.

Thanks for your input. I will put this aside as a possible experimental round.