The .303 used by France for Aircraft MGs (Mostly FM Lewis) in early WW I ( 1915-16) was Imported from Britain, before France began its own production of .303 Ammo as new Ammunition.
France also imported “special” projectiles such as .303 Tracer and Armour Piercing from Britain.
They found that the US Contract-made ammo , as delivered, (without Primer Crimps) would cause defects in Air-Firing use ( Primers popping, etc and Gun synchronisation) so the Initial import batches of USCCo 15, etc, were “Reworked” and given primer crimping ( 3 or 4 stab crimps) in a French Factory.
As some of the Loadings of this import ammo was also not suitable for High altitude use, some of this ammo was also broken down and reloaded with new French-made Rifle-cartridge Powder , the primers crimped, and the Special Bullets used.
Then there is the situation ( “R^L” marked cases) where France also imported British-Made primed Cases for Filling and Loading in France, to French specifications for use in Aircraft MGs (Both Lewis and Vickers, and later, Darne Guns). France continued to use “7,7mm” as its aircraft calibre until development of the ?MAC 29/31 Aircraft Guns in 7,5mm Cartridge in the early 1930s.
BY 1917, France was producing its own .303 ammo ( Cartouche 7,7mm), and the reliance on British-supplied Ammunition and Components finally ceased by 1918.
BY late 1917, US contract .303 was also being supplied from the USA with primer crimps applied at the US contractor; But in any case, other “Problems” led to almost all the US-made ammo from WW I to be used in Bolt-action Rifles only ( and some Light machine guns) and after WW I, it was disposed of ( to Portugal, Baltic States), as the US Powder also had “shelf life” problems…almost a Billion rounds of various .303 ammunition was dumped in the North Sea in 1919, as not even being fit to give away to friendly countries.
BTW, PS: all the Cases with the added “3&4 stab crimps”, at least 1915 & 1916 and early 1917 dates are French Modified…Britain in its supplied R^L and R16W ( Rudge Withworth Cycles) cases even if “ring crimped” were over-struck in France as well. I would suspect that the 1916 British cases were dismantled ammunition, rather than "component " cases, but I am unsure with regards to theses British cases.