Essentially those would under normal circumstances be useless against shinigami and hollows. But taking into account verse equalization, it wouldn't matter much. It's overwhelming fodder that deal with guns and cannons in One Piece. Only a few stronger characters use them, presumably in conjunction with haki like Benn Beckmann and Izo. Also I think this should be directed at Naruto not Bleach as Kishimoto himself said that guns would be too much for the Naruto world to handle. I presume he wasn't including the Jinchuuriki and pasts legends like Madara and Hashirama.