The newer powder produced higher pressure. Add the mag prime and it over SAAMI pressure.
Years ago i started with 14 grs , mag primer. Now loading 13 grs with a (158) 163 gr lswc plain base. Powder lot makes a difference, old vs new. Link is proof to me.
I read the article and it was very interesting. I see a huge difference in the pressures, but one thing that caught my attention, was depending on whos data you look at, only one of the loads he listed and I think it was with the Winchester primer was over the max pressure that is listed by Hodgdon. The newest Hodgdon data list the max load of 158gr XTP is 16.7gr of H110 with a pressure of 40,700. All of the other loads he posted are under the max pressure stated by Hodgdon. While I use magnum primers in all my loads, I'm very careful about working up to max and almost never use max powder charges listed.
At the end of last summer and into the fall, I was doing some unscientific testing on primers and my testing was magnum vs standard primers for target loads. What I was testing was difference in consistent velocities as well as accuracy. No of my loads were anywhere near max, so pressure was not a concern. all were with 38 special and only a few were approaching +P range. Then my chronograph was stolen and I have not had enough time to shoot much so I haven't replaced it. Here is what I did find before stopping. The majority of my target shooting consists of 3 Powders. Bullseye, Universal and HS-6. I only use Federal Primers since some of my revolvers have very light actions and CCI will not ignite 100%.
Here is what I did find.
One disclaimer. Accuracy was me shooting off a rest. I'm sure off a Ransom Rest it would be more scientific, but I don't have one. I'm certainly not an expert marksman, but can hold my own with a Revolver.
Bullseye.
Using the sold stand by load of 3.0 gr. with 148gr swaged HBWC and also 158gr SWC both regular lead and HyTek Coated.
No noticeable difference in accuracy from standard to magnum. Accuracy with Bullseye Loads was at 15 and 25 yards.
Magnum primers did give a slight edge in more consistent velocities (less of a spread with magnum) but only slightly better.
HS-6
Tested Several Different bullet weights and charges. 130gr HyTek Coated, 158gr SWC Lead and Coated and 158gr FP Coated.
These were tested at 25 and 75 yards for Accuracy.
Magnum Primers preformed much better with HS-6 no matter how light or heavy I went with powder charge.
A bid difference is velocity spread. Magnum Primers had much less spread than standard in all loads I tried.
Accuracy was about the same with either primer at 25 yards. Close enough to call even.
AT 75 yards, the accuracy was much better with magnum primers. Of course you would expect that result with the velocities being more consistent.
Universal
I use more Universal than any other Powder, so I spent a little more time here.
Tested bullet weights were 148gr HBWC, 130gr Coated FP, 158gr SWC Coated and Uncoated, Berrys 158gr THP, and Speer 158gr FMJ Plinker
Results were much like HS-6 but not as noticeable of a difference from magnum to standard. Sort of in between
Again, accuracy at 25 yards was a toss up but accuracy at 75 was noticeably better with magnum primers.
My testing may not help anyone and/or change the way you do things on your bench. I know what was posted above was more of a comparison on pressures for safety purposes which I'm all about. My testing was really about accuracy and consistency which really go hand in hand.
I think one of the problem with a lot of reloaders out there today is trying to push everything to the max and this is what causes people to get hurt. The data posted above about pressures did certainly open my eyes. Most of us veteran loaders by now have worked up there standard loads that have worked for years and at least for me, the quest is to squeeze out a little more accuracy not fps. If I want something hotter than .357mag, then I go to the 41 or 44 mags. No sense in being unsafe just for a little more power.
My conclusion to my testing is that I will continue to use magnum primers for everything since I see a tad more accuracy. It also may have been a little bias testing since I have about 30k Federal Magnum SPP on hand. Any comments favorable or critical will be appreciated.