I discovered the flanges are not always rolled with even thickness on Ludwigs so I decided to take the shell thickness measurements through the lug holes. Notice how on the Ludwig seamless spun shells the spining action of the machine rollers squeezes the material so that more ends up nearer the top of the shell, in other words the thickness across the shell is tapered. Whether that was accidental or intentional with the machinery available at the time I have no idea but there's no doubt it works sonically! "B" represents the top edge on the top lug hole and "A" represents the lower edge on the bottom lug hole. I'll add to this as more shells are measured. Below is a video of a seamless Sonor shell being made which should give a genral idea of how these types of shells are produced.