Necked down 5.7FNH case.

10.0gr AA1680, 20gr V'max: 3460fps.

Have two, my own with help: NEF, .17HMR barrel on a .223 action. Don't DO IT!! Too much details in the tiny parts that are sintered not steel and break.

Cooper M-38: FINE all the way.

Also known as: 4.4x28mm.
See: foxhunter .17 Velociraptor on Saubier.com. He did an extensive load development for this gun and it's all posted there.

George

Isn't the 5.7 case the one that is coated in polymer of some sort, and as soon as the polymer is gone the round won't feed? I guess maybe not an issue in a bolt action rifle or the NEF single shot, but something that makes me shy away from the original round. I won't own something I can't handload for...