Emike, thanks for answering. Even when viewing the enlarged version of your shell photo, I could see no trace of a bourrelet at all. But I did notice your shell appears to have the same sabot as the 2.9" Broun-Body Read.
About the casting flaw bubble next to its fuzehole:
Pardon me please, but I have to say your guess "that in flight a thin iron cover over the bubble melted away exposing this large hole next to the fuse hole" is impossible. Iron melts at something like 2,500 or 2,600 degrees Fahrenheit.
Which brings me to my answer about the alleged wide-open casting flaw airbubbles getting passed by a Confederate Ordnance Inspector. Nope... the bubbles were covered by a thin shell of iron. They were not externally visible. When the fired projectile strikes the ground, the impact crushes the thin iron which covers the bubble, exposing what was until then a non-visible casting flaw. Or, in the case of Mike O'Donnell's Mullane/Tennessee-Sabot shell, firing blast crushes the thin iron covering the airbubble(s).
Extra-close inspection will reveal the broken edge of the thin shell. For anyone desiring proof... in my own collection I have a 3-inch Hotchkiss basecup, which has a 1.5"-wide-by-.5-inch-deep Frisbee-shaped airbubble at the center of the basecup's rounded exterior. That surely would not have been passed by a US Ordnance Inspector. The broken edge of the covering iron "shell" is clearly visible.
I've also owned an 18-Pounder Solid-Shot (a RevWar one) which had a ping-pong-ball-sized casting airbubble that got exposed when the ball struck the ground. Again, the broken edge of the covering iron "shell" can be seen. (Some of you who've visited my house in the past may have viewed that ball in-person.)
I've also got a 2.9" Read shell's exploded base, with a big "Frisbee" airbubble where the lathe dimple used to be. The shell could not have been lathed if the bubble was visible there when the shell was connected to the lathe. In other words, if the airbubble was visible, the lathe dimple would be in the bottom of the airbubble. But the lathe dimple is absent.
We know that when casting-flaw air bubbles were visible, and thought to be large enough to potentially cause a problem when exposed to firing-blast, the hole was patched with lead. I'm sure some of you guys have seen examples of that.
For additional proof, if any is still desired, see the photo of a sawed-in-half 3" Hotchkiss Percussion shell in the Melton-&-Pawl booklet, on the left side of page 13. For those of you who don't have the booklet, go to civilwarartillery.com and select "Field Projectiles" and then "Cross Sections," then scroll down to the sawed-in-half 3" Hotchkiss Percussion shell. The photo clearly shows a HUGE and ENTIRELY INTERNAL oblong-shaped airbubble across nearly the entire bottom of the nose section... which passed Inspection because the airbubble is covered by a thin shell of iron.
Regards,
Pete