A conventional WAD with a different type of lid could not store a 16.68mm iron ball, but this product is different! It is very difficult to store 10 6mm BBs, so I use a 16.68mm diameter steel ball or resin ball, but the iron weight ball is more powerful and fun. You can enjoy the same recoil as when you shoot a small real gun. Paintball bullets seem to fit just fine, but they are expensive in Japan, so I use cheap resin or iron.