Never heard of a .22 pellet trainer?
The British tried out one based on the No4. In fact it WAS a No4 with a barrel liner but a .303 chamber so it could be loaded with chargers like the regular rifle. You pumped up the cartridges instead of the rifle and inserted the pellet in the end of the cartridge.
I have a commercial one that was produced after they went back to the standard .22
175pounds plus a "shooters pack for another 55 quid that included the pump, 5 cartridges, lube, and 100 aluminum bullets.