Changing Calibers The Blaser R8 is a modular system capable of switching barrels. When changing from one caliber to another within the same caliber family, no bolt head change is necessary. If going outside of the caliber group during a barrel exchange, the bolt head has to be changed as well. However, the bolt head can be exchanged quickly and easily. NOTE: Except for the Blaser Saddle Mount, no R8 components are interchangeable with R93 components. Blaser USED R8 Standard Barrel 204 Ruger R8_BR5N_204_23 - Open Box, No Magazine Insert UA4552