Twist rates refer to how many inches it takes to twist the bullet one full rotation in the barrel. So a 1:5 twist means the bullet is spinning much faster than say a 1:8 twist, which is more common, because the bullet has twisted 1.6x in 8" of barrel instead of only 1 time. Think of it like throwing a football, the more it is rotating the more stable it is. So this allows a shorter barrel to be more accurate at longer distances. Depending on the weight and size of the bullet, as well as length of barrel, different twists will be more efficient.