Jim, I just rechecked Houchin's book, and all the HOT information in it is just copies of Hunter Arms advertizing. That is about what I expected, as John wasn't particularly mechanically inclined. I would be very surprised if the D and S on your trigger meant doubles and singles, as I believe that the 10 gauge had been banned from trap or live bird shooting by the time your gun was built. I have never seen or heard of a HOT that was set up in any way besides selecting right first or left first, but I have a Tobin trap gun with a single trigger that is set up so that it fires right-left in one position, and left only in the other. I originally thought it was broken somehow, but when I took it apart to check it, I found that it was built that way and could not be changed. Trap shooters must have always been a strange bunch!