Gun damage rate

Problem is guns damaged is from the game you played. Should it be based on the bullet it shoots?
I was once very happy to enter some game at end and win it without even trigger, a free 5 GP, but not now, last night I found that even a gun is never used, its still damaged after several games.
I think it is reasonable for me -- z8 can make the gun bought from GP have more damage in each shot, while the special weapon damages slower.