From our friends at Teufelshund Tactical:

Let’s talk about the quality of H&K barrels for a moment. That’s a P7M13 barrel and that’s a hollowed out bullet, not an empty cartridge casing. My customer sent me their pistol because he had a squib round, which is caused when an underpowered bullet fails to leave the barrel and the next round fired impacts behind it. In this instance, the initial bullet was actually split, with the following bullet moving through its center and leaving its open center stuck inside the barrel. In a lesser quality barrel, you would have seen catastrophic damage to that barrel and most likely the slide and receiver, but with this H&K barrel, there isn’t even a scratch inside. Cleaned and reinstalled and ready to be shipped back to the customer.

When you buy H&K, you buy quality.