Entirely possible on it being the Gras cartridge, unfortunately the rim measurement is almost identical on both, the forward portion would make identification easier and that is pretty much gone. The headstamp would be the key to definite identification, a posting on one of the French military arms forums would probably clear it up. The numbers on the headstamp are the year of manufacture of that particular cartridge. The 4 on the left side designate the fourth quarter, opposite is possibly a 6, if it is a 6 it was manufactured in the 4th quarter of 1906.