General Failly, the commander of the French expeditionary force in the Papal States, notoriously commented in his dispatch after Mentana that “nos fusils Chassepot ont fait merveille” (our Chassepot rifles have done wonders) for which insensitive remark he was taken to task by anticlerical and liberal critics both in France and Italy.
Interestingly, not all the French soldiers at Mentana had the Chassepot. The French contingent in the Franco-Papal army was in brigade strength and the infantry component consisted of one battalion each of the 1st and 29th Line Regiments, two battalions of the 59th Line Regiment and the 2nd battalion of Chasseurs à Pied. The chasseurs were not issued with the Chassepot until 1868, but apparently their expert marksmen made just as good practice at Mentana with their rifled muzzleloaders as did the lignards with their Chassepots.
There remains a degree of controversy in accounts of Mentana as to how far the Franco-Papal victory was due to the superior weapons of the French contingent, and how far to the fighting qualities of the Papal Zouaves, whose finest hour this clearly was.
The following film sequence is a strongly pro-Papal celebration of the victory at Mentana, with plenty of good photos of the Zouaves.