The groove diameter of the 7.62x39 is .3105, and the PSA barrels are sized to that approximate diameter.
From much research and field experience, all of the 123gr-125gr .311 bullets currently available will expand properly at 7.62x39 velocities. It’s when you start getting into the 150gr and heavier bullets that reliable expansion becomes more problematic.
The Sierra 125gr Is a little tougher than the Hornaday, which is pretty soft. Both will work well on deer, and the Sierra works well on hogs. The largest hog that I took with the Sierra 125gr was probably 500 pounds, and at spitting distance the bullet penetrated shoulder to shoulder and stopped under the hide on the off side in a perfect mushroom.