Get the shirt here: https://shop.bbtv.com/collections/forgotten-weapons/products/unisex-t-shirt-51
When the Modele 1890 Berthier carbine was adopted for the French cavalry, the decision was made to produce a special version for the Cuirassier troops. These were the elite heavy cavalry, equipped with steel breastplates and elaborate plumed helmets. They existed in that very brief window where the worlds of Napoleon and the smokeless-powder rifle coexisted.
The armor worn by the Cuirassier required some special adaptations to their firearms, specifically to the stocks. The scaled chinstrap of the helmet interfered with a normal cheek weld to the carbine, so the comb was removed from the stock. The metal buttplate also was a poor match for the metal cuirass, as it was difficult to hold the gun in position to aim. To account for this, a leather buttplate was used on these carbine, which would be much less slippery on armor.
Aside from these changes to the stock, the carbine was identical to the standard 1890 cavalry carbine. A total of 20,000 Cuirassier carbines were made in 1891 at the Chatellerault arsenal, and few survived World War One. By fairly early in 1915 the cavalry units had been repurposed as infantry, and the Cuirassier went into the trenches with the armor and carbines - perhaps better equipped, ironically, than the infantry in the greatcoats, kepis, and with Lebel rifles.
Thanks to Justin for finding this rifle for me!