I'm having an issue with one of my semi-auto PPSh41 rifles. One in about every 10 rounds doesn't light off. The seller says the off center strikes aren't a problem, but I disagree. I'm not 100% on the internal structure of the primer, but I thought the firing pin had to hit more or less in the center to crush the primer against the anvil. I'm not sure enough about that though. Most of them look like this. Some are closer to or further from center depending on how the bolt settles.