Hi Dave, I spent a while searching, and came up with not alot!. Hardly worth waiting for.
But for what its worth, these are my thoughts...
- The 8,8cm proof projectiles Ive seen are pretty much flat topped, as are most of the german proofs in this thread (
http://www.wk2ammo.com/showthread.php?3287-German-WW2-Proof-shot-gallery&highlight=proof+shot) and they dont appear to have grooves. (When did grooves start appearing - Pre WW1?)
- The only other 8,8cm I can think of is 3.45in/25PR which doesnt seem to fit, so focussing more on 90mm
- The style and (sintered'y looking) texture of the driveband has a hint of American about it, but then the K would probably be replaced with lb if it is indeed the weight (which does seem likely as a 90mm projectile is around 10kg and visually half the length)
- The drive band reminded me most of the 53mm Gruson and a little of czech rounds, and ended up searching Gruson, Škoda, Hotchkiss etc.
Ultimately no joy, best guess is 90mm proof for French Mle26 Naval or Skoda kanon vz12/20.
Rich