I’m in the process of developing a new load for my .338wm. In South Africa we are limited to very few powders so I’m using approx. 70gr of our local Somchem S365. According to their manual they recommend CCI200 primers for a 250gr bullet. My thinking is that CCI250 or magnum primers would give better or more consistent ignition. Is that true? Could I expect a major increase or decrease in pressure?

Thanks for your help on any of my topics. Being quite new to this (12months or so) your advice and comments are priceless.

Cheers
Johan

Johan, you may just have to try both kinds of primers to see what your gun prefers.

I have loaded the .338 Win Mag a good deal and generally find that the magnum primers work best. This has proven true with such powders as H 4831, RL 22, IMR 4350, H 4350, etc.

BUT, when testing RL 19 in the .338 Win Mag I found that standard primers shot the best and gave a better Standard Deviation over the chronograph. I tried this with both Federal and CCI primers, the standard primers gave better performance every time with RL 19.

If there is to be any pressure differences, the magnum version such as the CCI 250 SHOULD give a little higher pressures.

You are unlikley to find much difference in the performance of the two primers. Use the 250's if you like. The only advantage of "magnum" primers in cases the size of the .338 is for better ignition in very cold (like 0 degrees F) conditions -- not much of an issue in S. Africa.