You don't use much air in a pistol - so a pump is fine.

But.......unless it's only for very occasional use, a bottle will be a whole lot easier and quicker and not too much more expensive second hand than a pump? It will also do a huge number of fills for a pistol.

Why make things hard for yourself, the difference in cost over the years is pennies, but the pumping is arduous, and spoils your aim for the next 20mins also.

James