Dear GN, From reading the equipment lists of the matches it seems that Bartlein and Krieger are most often used for 6mm barrels. Twist rates usually vary between 13-14 twist. The blanks are expensive and the wait times are long if you order from the manufacture. You might try places like Bruno's who often have the barrels in stock. 22 and 30 caliber barrels have a larger number of manufactures used by BR shooters.