The use of small primers in large-capacity cases is for consistency and accuracy. The best illustration that comes to mind is the .22 CHetah (CH for Carmichael-Huntington). It is essentially a .308 Winchester necked down to .22 cal. Jim Carmichael had .308 cases made, with a small rifle pocket, in the belief that the small primer would yield more consistent ignition, and better accuracy. His subsequent testing seemed to bear this out. I might add, that this was in a Benchrest-type gun, where every little detail is scrutinized, and tolerances are held to absolute minimum. It is unlikely an"ordinary gun" would see much benefit.
This will, in no way, increase the pressure-handling abilities of a particular weapon or cartridge. It matters not, from a pressure standpoint, whether the primer pocket is large, or small. For a given velocity, with a certain powder/bullet combination, in a particular weapon, you will get "X" amount of pressure, case back-thrust, and strain on the gun. F'rinstance, it doesn't matter if you use 2gr less powder, and a magnum primer, or 2gr more powder, and a standard primer; if the velocities are the same, the pressures are the same in that gun.
Sorry for running on, but I don't wish to see you hurt trying to overpressure a cartridge just because it has a small primer. Pressure is still pressure.>>>>>>>>>>>>>>>>Bug.
