Primers and Powder go together like mixed drinks, or like chips and dips. There are lots of chips, and lots of dips, but you likely have your favorite combo.
Primers have different burn rates the same as powders. Some combos go together better than others.
Buddy and I have DW Revolvers with consecutive serial numbers. They are alike as can be. One day we were developing loads and had come to the range together. When we chronographed the loads they were within a few feet in velocity. Good SD and spread. I was using Rem 7 1/2 primers and he was using WSR primers. Same powder, but he was using 2.0 grains more than I. Different combo with similar results.
I have a 7TCU in a Remington XP action. Used WW748 for years. Was getting low on supply so opted to use a different powder as I couldnt find any 748. Worked up a load with H335. With my standard Rem 7 1/2 primer I was shooting 5 shots within an inch at 100, but the gun was capable of doing better. When I got home I loaded up same load, but tried 4 different primers. Like the original post, one primer stood out, and my group went from @ 1.0" to sub .5". H335 in that gun, does better with the WSR primer.
If you are working up a load, primer and powder selections are important. You have to use the right combo.
Yes, I have lots of various primer brands, so I can match all the different combos with powder.
Good luck. The search is half the fun.
Steve