It seems that such rifles did exist
GRAS en 22LR reglementaire - Page 4
- although, as you can see if you follow the thread, the Frenchthemselves are not all convinced that this was a "fusil reglementaire" i.e. standard rifle. The standard Gras cadet rifle was basically a normal Gras with an altered chamber to take shorter (50mm long) cartridges.
In order to save money, a real cadet training rifle in .22 short was introduced ca. 1880, - blackpowder days!!! - and as far as I know it was the world's first purpose-built small-bore cadet training rifle, as opposed to an adapted or relined full-size rifle. I have one. It is also marked up in military style, with all parts numbered - including barrel bands and buttplate - something which would not be done for commericial guns. The number is above 5000, so there is little doubt that this was a standard item. I have shot it in France and shown it to members of the French blackpowder shooting team, who confirmed its origins.
If you read the linked posts, it appears that the barrel on the lined Gras was shortened by about 4" to reduce the weight, since the liner increased the weight considerably - a smaller hole in same OD tube = more weight. But a lack of numbering of individual parts suggests a commercial relining, rather than a military alteration.
I strongly recommend that you somehow arrange for photos to be taken and posted, then we can let the French shooters have a look and give their opinions.
Hope this helps
Patrick Chadwick, Membre des Arquebusiers de France