Stamping, Whilst in the Midst of a Barrel Roll is some difficult. The "G" load is all wrong and there is also a torque load at the long axis of the airframe. If not well anchored, the appendages will flail. Much much easer to do in a Chandelle.
No, not actually of any pertinence to the OP. But what the heck. It's a quiet Sunday morning and I slept late cause I was traveling/shooting/traveling all of yesterday (Very GOOD match too). So, should the masses choose to ignore my contribution to the issue, feel at ease to do so. I won't be at all offended