I guess it would depend on how the word was being used. If you are referring to a "gallery rifle", these were, I think, intended to be used with low-power cartridges for gallery shooting, such as amusement partks, indoor ranges, etc.
The term refers to relatively small, light rifles of small calibers. The cartridges are so small and weak that the facility where a competition would have been held did not require any special equipment like reinforced back stops and so the shooting events took places at the ranges, pubs and other indoor public facilities.
I think of the rifle like the Remington 24 in .22 short which was common in shooting galleries at arcades. There was a light weight bullet that was made from a clay material...haven't done the research, but they were something like 15gr. in weight.