Do you get two shots at the bird?

No, that would give a disadvantage to the shooters of single barrel guns!

They would have to reload fast. I had read where vintage trap you had full use of the gun hence the question.

This is about as vintage as you can get:
February 12, 1883, “The much talked of Kimble-Kleintz shooting contest took place at the Shooting Park, several hundred sportsmen from all parts of the state being present ... The match was for $500, the Peoria club backing Kimble against the noted Philadelphian, at 100 birds, thirty yards rise, ground trap, each contestant handling and trapping for his opponent and only one barrel to be used.

If any of you gentleman and ladies are headed to our local shoot at MRC . I will be there from Wednesday until Saturday , look me up. Our youth trap team will have a tent there and if I'm not there, most of the other volunteers will know where I'm at. Looking forward to a great week of shooting. Lee

I'm looking forward to the shoot as always. I have the use of a DHE straight grip with 34 inch barrels. I'm not a trap shooter but am looking forward to giving it a try both at trap and the pigeon ring.

I think you need to specify a little more about a single barrel gun. You probably mean a break open single barrel. I think by definition a Winchester Mdl 12 or any other pump gun would qualify and I'm not sure that is what you intended to allow. At our vintage trap and skeet shoot in Pa, a pump gun is not allowed no matter when it was produced.