A firearm with a barrel that uses an ammunition discharge chamber that includes improved throat located between the chamber's free bore and the rifle bore. The improved throat includes a relatively short, inward aligned first step, an intermediate elongated cylindrical body, and a longer, inward aligned second tapered step. Formed on the inside surfaces of the first step, the elongated body and the second step are rifling grooves and lands that gradually their depths and heights from rear to front direction. The two steps are tapered inward between 1.0 to 1.5 degrees. Using a short first step, an elongated cylindrical body with straight sidewalls, a longer second step with continuous grooves and lands that begin gradually in depth and height from rear to front directions, chamber pressure is reduced thereby enabling more gun powder to be used and bullet misalignment in the rifle bore is reduced.