The process starts with drawn wire, which is where the uniformity comes from. Every particle will be cut from the same wire, of the same alloy, with the same drawn structure, so the variation that a casting process introduces is never present to begin with.

Cutting is to a length equal to the wire diameter. That produces a cylinder whose dimensions are set by the wire rather than by a screen, which is why cut wire does not need to be graded into size fractions the way cast shot does.

Conditioning follows for media intended for peening. The cylinders are tumbled and ground against each other until the edges are removed and the particle approaches spherical. How far this is taken is a specification, not a single state, because different peening standards call for different degrees of rounding.

The consequence of all this appears months later, in the operating mix. Media that started uniform wears towards a narrower distribution than media that started wide, which keeps the finish consistent and reduces the fines the separator has to pull out.