Do you guys think it would be possible to manufacture an upper in .17HMR for an AR15. The part I can't quite figure out is what type of magazine it would load from? ANy idea's or thoughts on this subject?

Given the fact that you can purchase .22 LR rimfire uppers for an AR it might be possible to get a custom builder like Kurt's Kustom Firearms to fabricate something along these lines.

Doesn't hurt to ask.

You could get a .17Rem upper built and roll your own ammo down to 17HMR specs (2550 fps muzzle velocity) with the 20 grain V-max instead of the 17 grainer that is being loaded in the HMR ammo.

Doesn't make much sense to forsake one of the strongest attributes of the .17Rem and slow it down though.