Buck Hamlin of Pevely, MO has done many HOT single trigger to double trigger conversions and does great work. Buck has done one such conversion for me; an early 5E that had been poorly converted from an original double trigger gun to a single trigger using a HOT trigger unit. That said, I don't know why you'd want to eliminate the factory original HOT trigger and lower the value of your gun. If the trigger is not functioning properly, the problem is most likely very minor; and Jerry Andrews of West VA can repair any Hunter HOT trigger problems you may be experiencing. Jerry repaired a HOT trigger issue on a Grade 3E Smith I owned and I never had another problem with that gun. If you visit the L.C. Smith forum, someone there will give you Jerry's contact information (and I'm sure Jerry could do the single to double trigger conversion if you do go that route).
