Magnum primer on 243AI

[Chrisjan]

I have a 26" krieger, using Somchem S365. Winchester brass and Nosler 70gr BT.
Neck tention is 0.003.

S365 is an extruded stick powder as H4350

Quickload gave me a node on 3680fps, I could only get 3640fps. Upping the charge gave me a lower speed. This was on federal 210m primers.

So I changed to Federal 215m magnum primers. On the same 48gr charge it gave me 3800fps. A full 160 fps more on primer swop.

Should I stay with a good case fill and magnum primer or go to a faster powder with less case fill but standard primer?

 

[Lefty7mmstw]

I have a 26" krieger, using Somchem S365. Winchester brass and Nosler 70gr BT.
Neck tention is 0.003.

S365 is an extruded stick powder as H4350

Quickload gave me a node on 3680fps, I could only get 3640fps. Upping the charge gave me a lower speed. This was on federal 210m primers.

So I changed to Federal 215m magnum primers. On the same 48gr charge it gave me 3800fps. A full 160 fps more on primer swop.

Should I stay with a good case fill and magnum primer or go to a faster powder with less case fill but standard primer?

From what I understand, quickload is not 100% exact(I haven't used nor will I) and 40 fps off is actually rather good as far as data versus reality.
I've used the 215 in regular 243's before and done rather well, but you still have to remember that you can't push faster than "book" velocities without elevated pressures. Think of the estimated velocity as a speed limit if you don't have pressure testing equipment on the rifle. You can get fuzzy a few fps, but more than a percent or two fast is probably rather high pressure.
It's better to stay with the normal primer in a smaller case like the 243 unless you are using ball powder. I was getting a 100 gr bullet up to speed in a striker pistol and needed pressures up quick.