That’s .45, presumably .45 ACP, AKA 11.43×23mm.
http://en.wikipedia.org/wiki/.45_ACP
I wouldn’t think that a particularly common caliber in France.
I visited Nice a couple years ago and happened across a small guns/weapons shop and went in, looked around, and chatted briefly with the proprietor. He really had very, very little on hand, and was very envious of our gun laws.
Thanks for those details, most informative. I believe that gun control is quite strict in France, although of course, those outside the law always manage to get weapons.