The risk is even greater with straight blowback guns. If a squib blocks the barrel, there can still be plenty of gas pressure enough to cycle the action and get another round in the chamber ready to fire. It feels like everything has happened as it should, including blast noise, so you keep pulling the trigger.
A friend with a semi-auto Thompson 1927 was firing Wolf steel case FMJ through it about 13 years ago and had that happen to him. He lodged 5 bullets in the bore before the barrel split, not realizing what was happening until gas vented up and down in a way that caught his attention through the sights. Fortunately, the Thompsons are so over-built, I was able to pull his old barrel off and screw on a new one, with nothing else needing any repair, and it chugs along still today. (I saved the remnant barrel and had it bobbed about 4 inches back behind where the visible crack started and then threaded .578x28 with only about 5 inches of total barrel length. One day I'll finally get around to making a whacky ultra-shorty SBR Tommy that I can hang a suppressor on.)
In these photos, you can see where the gunsmith he originally took the gun to put it on a mill and milled away some of the split barrel to get a better look at what had happened.
My buddy submitted a claim to Wolf for the damage the gun suffered, but they declined to compensate him at all. They said he should have been aware after the first round that something was wrong and should have stopped shooting, and that when he didn't, all liability transferred to him. Secondly, they also claimed that he should have sent the whole gun in original damaged condition to them for investigation, and that by having his gunsmith start carving away on the barrel, any chance to determine if they were truly at fault was destroyed, so they would refuse to accept blame. Both of those arguments would have been able to be defeated in court. But who's going to spend tens of thousands of dollars to win the point over a gun that could be replaced for just $1000 (at that time)? And Wolf knew it. But had someone been injured, that would have changed everything, and likely Wolf would have bent over backward at that point to try and make my buddy happy.
