I am loading for .243 Win, .270 Win, 7mm Rem. Mag., and .300 Rem. SAUM. If you have a preference for magnum or large rifle primers with any or all of these calibers, please let me know. Your info. is greatly appreciated.

The only thing magnum primers are going to do is make the mfg more money. They are like adding a pint of "Motor Honey" to your oil and thinking you're going to have a new engine.

This opinion is based of 45 years of reloading without them. NEVER a primer related issue.

.243 Winchester - Remington 9-1/2
.270 winchester - Winchester WLR
7MM Remington Magnum - CCI-200
.300 Remington SAUM - Remington 9-1/2M

Let see 243 large rifle,270 large rifle,7mag mag primer don't own the other so cann't comment. I mainly use Federal and once in awhile Rem primers.

About the only way to tell which load & primer combination your rifle likes is to load some up and try them. For example, in my .270 using 150 grain bullets, the 52.4 gr of H4350 with a Rem 9 1/2 groups at just under 2", but switching to Rem 9 1/2M primers shrinks the group to barely over an inch. For reasons that I don't understand, the load with the magnum primer chronys an average of 24 fps slower than the one with standard primers. There is no way to tell without actually testing the loads.