[JLA]

classic casehead failure Dan. Is it possible your friend that did the reloading for you bought some once fired brass from a local range? That is a very common issue with handloads in glock pistols. Its is also likely it was an overcharge. though i suspect if it had been an overcharge it would have also blown the primer out. Could have also been a setback. Maybe he forgot to crimop that particular round and upon chambering the feed ramp crammed the bullet deeper into the case and decreased case capacity causing a pressure spike. There are many causes for casehead failures. They happen in glocks due to the unsupported chamber. they happen in everything else primarily due to overcharges or using brass that was first fired in a glock and purchased form a once fired brass supplier.