Someone should do test firings to see if there is still enough energy to cycle the bolt reliably.
9" is almost halving the barrel length.
But actually, by the muzzle energy numbers at:
http: //ballisticsbytheinch.com/22.html
,the bullets might only lose about 3% of their energy from 16 to 9".
So I guess this would not be a concern, unless we got down to sub 6" barrels.
Still, might want to go with not just HV, but hyper v rounds, I'd favour CCI Velocitors.
Correction: Velocity declines by only about 3%, but the Energy declines with the square of Velocity, and the actual muzzle energy drops by more than 3%. For Stingers or Velocitors is looks like approx 160lb-ft vs 145lb-ft.
ballisticsbytheinch.com/2011graphs+/22ME.html
Still not a huge drop, although the energy of the bullet does not necessarily equate to the energy that the bolt & recoil springs see, so testing is of course best way to know.