I have read that the German MP5 barrels were designed to survive squib loads, where a bullet is stuck in the barrel and hit by another. Squib loads are a problem with full auto's because if there is enough pressure from the squib to work the action and feed a new round, there is no pause for you to recognize the squib shot and not send the next bullet down the barrel. I personally experienced this with an MP5. The barrel swelled just behind the front sight post and actually shot out the squib with the following round. The MP5 continued to function for numerous rounds after that, with no change of point of impact and no burst barrel! Good old German engineering!
