These .22" Knuckle-Guns are French:

I've found two makes of these handy whackers dating from around WWI .. 'Le Poilu' & 'Le Centenaire'.

'Le Poilu' Means "Hairy Ones"

 - The Name For French Soldiers From The WWI Trenches:

Le Centenaire Knuckle Gun.

"COUP de POING" = 'punch, knuckle duster' 

- But What Do The Dates Signify?

Both of these single shot guns are "chambered" with smooth bores for .22" short rim-fire rounds which would likely not do very much good .. but better than nothing?

 - It appears that it's actually the hammer that holds the cartridge into the chamber.

Le Centenaire's Action.

Le Poilu Internals.

The French name for ordinary 'brass knuckles' or the knuckle duster is "Poing americain" .. 'american fist'. (Brass knuckles were used by President Abraham Lincoln’s secret service aids.)

"The stereotype of the French WWI soldier "Poilu" was of bravery and endurance, but not always of unquestioning obedience. At the disastrous Chemin des Dames offensive of 1917 under General Robert Nivelle, they were said to have gone into no man's land making baa'ing noises—a collective bit of gallows humor signaling the idea that they were being sent as lambs to the slaughter. "

As far  back in history as "Ancient Rome" - hardened knuckles are recorded as giving an advantage to the combatant.

Roman 'Cestus' or 'Caestus'

Some Old 'Knucks'

Coup de poing Advert from 1902 - For Cyclists.

Marty K.