I just got a used p 95. i took it out fire 50 rounds of bulk ammo ( I have no idea of brand or any thing ), it was the dirtyiest ammo i have ever seen. All round fired great except the last 2, i had one ftf but a slap on the back of the slide fixed it. and after the last round fired out the slide did not lock back. can i say this was from dirty ammo or should i be worried?