From the FWIW department: A source with connections to the French MoD says their special forces purchased 6mm ARC rifles and ammo, planning to do testing this year.

The rifles are reportedly the STT-15 with 18" Proof Research barrel -- San Tan Tactical | Blog - San Tan Tactical® 6ARC Collaboration with Hornady® and Proof Research®

Not always successfully, but France has managed to do some original thinking over the decades when it comes to military weapons. The 8mm Lebel cartridge and the Renault FT17 light tank come to mind.

A good friend was attached to a French armor unit during Desert Storm 1 and had nothing but praise for their training and ability. Their politicians not so much.