The primary arms micro with fixed base will co-witness. My experience hase been just low of dead of center for the co-witness with a choate front sight/ flash hider. The dot is so close to dead center that people who looked through it don't even notice. The single blade factory ruger front sight is slightly higher than the choate and according to Ultimak an Aimpoint micro will co-witness with that. I've seen pics of people using the Bushnell micro dot too with sucess but, I can't be 100%. The strikefire and sparc may ride too high for a co-witness. Keep in mind that the rail will get hot from the barrel and the cheaper the scope you use the higher probability it will malfunction from the heat. The Aimpoint is the best bet for durability but, my use of the primary arms has been fine. I also have been mindful of the heat and let the gun cool when I feel it gets to hot.