Premium rounds are often more accurate. On two separate occasions years ago when I was taking classes as a student while shooting drills all of the sudden my "groups" really tightened up compared to how I had been shooting... as in going into one ragged hole at some distance.
After the drill concluded & being a little puzzled cause we had been shooting all day & you kind of learn how you shoot, I dropped out my mag. & let out a small burst of light profanity... the Instructor came over & asked what was wrong.
I said," I just shot my frickin' Hydra-shoks that cost me $1 each!!!" I had been shooting Wolf which back then cost me $5.99 per box of 50.
The Instructor & the rest of the class thought my discomfort to be quite humorous.
No disagreement there. But most of us need to shoot 5 - 10k rounds of the cheapest ammo there to get trigger control and mechanics correct, vs buying $30 a box premium ammo and shooting it. In your example above, it was shooting ALOT of cheap Wolf ammo that made difference, not shooting one box of Wolf and then one box of Hydra-shoks. Ammo makes some difference, but not as much as repetition and lots and lots of trigger time.