[quote=“mausernut”]Fwiw: The painting could indicate the thing was meant to be fired in a rifled gun…? i.e. the sabots were meant to seperate from the arrow by centrifugal forces…?
The paint was to show any residual rotation if the sabot had slip rings for obturation…?
Soren, maybe not rifled since then the projectile would not need a “reversed cup” sabot design to aid sabot separation by creating the drag required. A “rifled design” would not neccessarily need such a feature (look at the early 105mm APDS of British design).
As you noticed correctly (to my opinion) the special “spiral paint job” is for better observation of possible rotation and evaluation of telemetric data later on.
If Jason is correct with his “extended neck” case design in 90mm and if it was intended to research the Soviet counterpart (and the design principles since it was the first smooth bore tank gun in service) this 90mm might have been a smooth bore too.
Slip rings: The fins on Jason’s 90mm have straight forward edges and are not angled. Many designs using slip rings in rifled guns have angled edges on the fins (the Russians use bending little “tails” on their folding fins on HEAT projectiles for example) to counter the residual rotation.
A fixed obturator ring is very important for smooth bores though. Maybe Jason can tell us what type of ring his projectile has on.
Just my thoughts…