5.7x28 case + 80gr projectiles = ???

[TheWizardOfOdd]

I got to looking at the 80gr Sierras and the 5.7x28 case and I thought, "Where have I seen this before?" Then I realized that the combination looked like a scaled down 240gr Sierra and 300 Whisper case. And that got me to wondering if it would be possible to use the 5.7 case as a basis for a subsonic 22 cal rifle. What do you think?

Until someone comes out with an appropriately scaled down bolt action I was thinking about having a Contender barrel made up. Put my can on the end and it might be a lot of fun. The questions I am left pondering are: How do I go about determining the proper twist for this project? I wonder what the external ballistics would be like with an 80 gr bullet starting out at 1040fps? And most importantly how come no one else (that I can find at least) has tried this?