If we ever see primers come back, I may load some 38spl cases with no powder, wooded dowel bullets, and crono different types of primers to see if there is any pressure difference between sp, spm, and sr. Some way to measure the heat would be handy though along with the pressure. Years ago I had a astm calorimeter but it is long gone now.I use SP in sub loads all the time,only lighting off 4-8grs.
That’s what the guy did in the video I mentioned. With everything else the same he loaded all three primers and there wasn’t a noticeable difference in velocity.Probably could just crono same loaded ammo with just differant primers and crono the results - any significant differance should show up in the data.
Your post reminds me of when I was a young man, working part time as a service station (back when they actually provided service). Remember the 1156 and 1157 light bulbs for cars? We would sell (and install) either bulb in your car. If you drove, lets say, a chevy impala, the bulb cost was something like $.50, if you drove a caddy, the bulb was something like $1.00, and if you drove a BMW or other high dollar car the bulb was something like $1.50. Same bulb but different price according to your car.I used to rep a factory that manufactured electrical receptacles (like in your walls) amongst other things. They had four different grades ranging from residential all the way to hospital grade and guess what? Other than the packaging and the green dot on the hospital grade they were all made of the exact same components, no difference in quality. It was all due to the cost of manufacturing and it was just cheaper to make the most expensive grade only as opposed to the cost of inventorying different components and the time spent setting up the machines. I would guess primers are probably in the same boat.