are small rifle and large rifle primers different diameters and specific to the casing or can you interchange primers to get different results just as you can vary the amount of powder?
Yes large and small primers are different diameters
There are standard and magnum primers in both sizes
The magnum primer,in simple terms has more fire to ignite larger quanites and or harder to ignite powder.
You can to a certain extent change primers to fine tune the load .
But you should return to a starting load and work up , because changing primers can change pressures .
Johnch