The cratering, or blanking, is not caused so much by the gap around the firing pin as it is by the size of the hole; this regardless of firing pin fit. There are other factors as well. A large hole of say .80" is likely to result in blanked primers at high pressure; even with a firing pin diameter of .0795. This because there is enough area for the pressure to act upon that it exceeds the ability of the primer cup to withstand the pressure. Now, if the firing pin is heavy enough, there may be enough inertia to support the cup adequately and prevent the blanking but the extra weight increases lock time, so there is a tradeoff there. If the boltface is bushed and the hole diameter reduced to .0625", the area upon which the pressure acts is nearly halved. This means there is only half as much pressure acting on the cup, which can easily withstand the reduced stress, even if there is a gap.
Firing pin tip shape can also influence the ability of the primer to with stand pressure. A hemispherical tip is easy on the material but offers a full diameter area for the pressure to act upon. A firing pin tip in the shape of a truncated cone with a rounded tip, providing the cone is fully outside the bolt face when fired, may serve to provide a stronger indentation of the primer, just due to the shape.
The depth to which the firing pin indents the cup also has an effect.
So, the bushing of the bolt face, along with the reduction in firing pin diameter will absolutely end blanking or cratering of the primer and will allow one to load to higher pressures. This is not necessarily because the fit of the pin to the hole is better; it is simply because the area of the primer which is unsupported is reduced. WH
