Thanks for all the replies. I'm doing two sessions of 25 gun mounts a day keeping both eyes open and it seems that the incidence of double vision is decreasing with practice. When I'm looking at the target I don't have double vision, but if I don't get a perfect gun mount and check down to the barrel to adjust I get some double vision about 50% of the time. I guess the solution is to keep at it until my gun mount is perfect every time, that way I will only be looking at the target and should be fine. As all the sources of instruction suggest, shooting clays as soon as I allow myself to get distracted by the bead I slow my swing and miss the bird! I'll keep at it for a bit and see how things go.
-DW