The HK MR556A1 w/ a Schmidt & Bender 1.1–4 x 24 Zenith Short Dot LE! Case closed, no other options.
http://www.hk-usa.com/civilian_products/mr556_general.asp
http://www.schmidtbender.com/scopes_policemarksman.shtml
http://www.hk-usa.com/civilian_products/mr556_general.asp
http://www.schmidtbender.com/scopes_policemarksman.shtml