I bet there is a huge drop-off in barrel pressure between when a bullet has just left the case and when it has passed the gas port.
Edit: I can see myself holding the gun where the forearm would be and carelessly getting a finger over the hole. That's the kind of luck I have sometimes.
Edit: I can see myself holding the gun where the forearm would be and carelessly getting a finger over the hole. That's the kind of luck I have sometimes.