5.7x28 Necked Down to a .17 or .20 Cal?

[jasonprox700]

Has anybody tried to neck down the 5.7x28 down to either a .17 or .20 caliber?  I think this would be a terrific little caliber for small game, and possibly even coyote and fox (depending on the ballistics, of course). 

If anybody has tried it, what kind of velocity are you getting?  Also, is there someone who can re-barrel a Five-seveN Pistol to either a .17 or .20?  Are there any other semi-auto pistols that can fire this round? 

[trotterlg]

Search for Velociraptor or some variation of this.  I did some work on a barrel for a H&R chambered for this, I have one sitting on my desk here in 17.  Here it is sitting next to a 22 Hornet.  Larry