Abstract: A paintball gun barrel assembly includes a muzzle and a shank assembly that is self-aligning with respect to the muzzle due to the interaction of complementary angled surfaces. The shank assembly may include a bore tube that removably fits within an insert housing and has a first bore and a first concentric angled surface on an output end thereof. The muzzle has a second bore and a second concentric angled surface on the input end thereof. Mating the insert housing, with the bore tube inside, to the muzzle portion engages the first angled surface with the second angled surface causing the first bore at the output end of the first bore tube to substantially align with the second bore at the input end of the muzzle portion. A plurality of different size bore tubes may be used, each having a different internal bore diameter, but the same outer dimensions.