If you are developing loads in a 24" heavy barrel AR, then you are using something very close to what I use in Highpower competition. I have a krieger on my space gun.
Primer choice is not that critical for accuracy, but as mentioned thin primers will pierce. I used sheaves of WSR primers when they were nickel plated. They were excellent. And then Winchester removed the nickel and made the cup thinner. I talked with Winchester and they told me that they had made the primers “more sensitive”. Which is something you do not need in a military action or a gas gun. The result of making the cups thinner is of course pierced primers at levels the old nickel primer functioned fine .
I had one slamfire in the AR, I dropped a round in the chamber, during the standing stage, and released the bolt. The round took a divot of dirt out in front of the firing line. It was a new brass WSR primer in the case. The next shooter on my point did the same thing, dropped a .223 round in with a Fed Match primer and also got a slamfire. Something to remember about AR’s, if you can, single load through the magazine. Another way is to trip the bolt release while holding the bolt back using the charging rod. Lower the bolt about half way then let go of the charging rod and bump the forward assist. It is always good practice to bump the forward assist on the first round, mag fed or port fed.
I do not shoot 52 matchkings. At least I have not loaded the bunch I have which I would only use at 100 yard matches. I shoot 69’s, 75’s, out to 300 yards, and 80’s at 500 or 600 yards. I test my loads with a chronograph and have found that in my AR’s I get ammunition that will not blow primers in 100 F weather at measured velocities ranges of 2800 fps with a 69, 2700 fps with a 75, and 2625 fps with an 80. Many folks push them faster, I don’t. You will get good accuracy and function with any brand of primer, you just have to test them on paper.
W748 was a very popular powder with the .223 and 308, but the market has moved on to other choices. I prefer stick powders to the ball, ball powders don’t seem to give much warning before they blow primers. Stick powders seem to have broader sweet spots. This is of course subjective. If you are considering other powders I recommend those in the 4895 burning range, such as IMR 4895, H4895, AA2495, AA2520 (ball) and N140.
My current primer choice in my match rifles is the CCI #41. I talked with a CCI representative, these are magnum primers and are mil spec. Which basically means they are “less sensitive”. This is great because I do not want the risk of another slamfire. Next time it could be out of battery, though that is unlikely. A military action, such as the AR, has lots of firing pin energy so misfires due to light firing pin strikes are not an issue. I have shot perfect long range scores with these primers, and my best Camp Perry Long Range scores with them. I am only concerned with on paper performance, not with theoretical issues of magnum primers and accuracy.
