I'm honestly not worried about an off center primer strike. The firing pin hits the primer cup, crushing the primer compound between the cup and the anvil (built into the primer for Boxer primers, built into the brass for Berdan primers).
I honestly can't see a significant difference between a direct on strike and an off center strike, the resulting detonation is going to happen REALLY fast. The hot gasses will then push through the flash hole (or holes in a Berdan primed case) to ignite the powder. Simply due to physical differences the resultant gas jet will have slightly different vortices due to the difference in firing pin impact.
Whether that translates into difference in accuracy I can't say, but I don't think it does. I think the difference in primer strength between primers even of the same brand and lot, are enough to have a bigger effect on accuracy than where the firing pin lands.
Machine guns are awesome until you have to carry one.