Emphasis mine. That includes everything called bullet, such as Bullet, Adamantine Bullet, Pitted Bullet, or Silver Bullet. Note that these are listed as specific items, sometimes with different abilities than regular special material weapons. There seems to be no restriction on crafting other types of bullets though, and, being bullets, they are price-reduced as well.
A full list of Bullet pricing can was compiled by Nefreet on the paizo boards. It's noteworthy to say that this list was copied to the PFS Shared GM Prep Folder's GM's Guide to Gunslingers (and PFS is quite RAW by design).