Add "enlarged or deformed" striker hole to the list.

Once you start rupturing primers, the problems accelerate. The super-hot jet of escaping gas acts like a cutting-torch and eats away at the striker and hole. This erosion causes further roughness of the striker tip and enlargement of the hole. Having a "perfect" striker tip and an oversized / out-of-round hole is also a recipe for rapid damage. This will often show up as little discs of metal being punched out of the primer cup by the annular jet of gas driving the work-hardened material rearwards. This, in turn causes more deformation of the primer cup, leading to even more gas leakage and cutting. Some WW2 production Arisakas are classic examples of this.

The deal is that the striker must have the correct form, smoothness and protrusion and the hole must be round and closely fit the the striker. It didn't matter too much back in the days of black powder. However, the pressures and temperatures at which smokeless propellants operate require much closer tolerances. One of the major feature of ALL military rifles that were developed in the late 19th Century it the amount of effort that went into diverting gas from ruptured primers way from the firers face. Note the vent holes in the Lee-Enfield bolt heads and the exhaust slots in a Mauser bolt. There was obviously a bit of an "issue" with such events, and the designers took it seriously.

An additional note is the ring formed at the diameter of the primer. If you are getting gas-cutting there, you may have excessive headspace. When the primer ignites, it tries to back out of the pocket. On a tightly headspaced, rimmed cartridge, this effect is small; on rimless cases it is quite noticeable. The only thing stopping the rimless case from moving forward is the relatively soft shoulder. This is why one should NEVER re-use cases used for very light loads as the basis for full-house loadings.

When the propellant charge ignites, the case is usually slammed back and forces the primer back flush with the head of the case.If you are using commercial ammo that has little or nor crimp on the primer, this action is quite fierce.This is one of the reasons military ammo generally has an annular retaining crimp on the primer pocket.
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.