Ok what is the difference between Small Pistol and Small Rifle primers? Let’s exclude the obvious such as pistol and rifle designations. The cups are identical outside diameter and the cup wall thickness is the same then is there a material difference? The anvil is different? Primer compound mixture assumption is that the rifle mixture is different with a hotter and longer duration ignition burn?

Did substituting small pistol with small rifle primers come into usage with the 38 Super and compensators?