I own one of these rifles and the double-set trigger hasalmost alwaysworked perfectly. I'm sorry to hear you are having problems. Problems with a new gun are really aggravating.

A couple of thoughts:

Check the rear lock retaining screw (the one that holds the lock in the stock). If screwed in too much, it will protude in to the path of the cock. You would think that would effect the firing no matter what thetrigger setting-just make sure the screw is flush with the lock plate.

It would be a good idea to pop that lock out and have a look inside. The wood work is pretty crappy inside my rifle, it probably is in yours. Check to make sure nothing is blocking the bearing surface on the trigger. Also have a look at the tumbler does it look like it is operating properly, that is do you see any obvious defects?

Something I was wondering, and I don't mean this as an insult, are you cleaning and lubricating the inside of the lock mechanism? The Shenandoah was my first flintlock and BP firearm, so I made all my mistakes on it. In the beginning I did not know you had to remove the lock and clean that as a part of your post-shooting clean up. Needless to say it wasn't long until the lock had all sorts of malfunctions. When I did finally take the lock out to clean it, it was full of crud. Cleaning and relubing the inside of the lock fixed the problem right away.

If you do decide to pop the lock out, DO NOT completely withdraw the forward lock retaining screw. Just loosen it enough to disengage it from the lock plate. That screw also holds the ramrod retainingspring in place.

One guess how I learned that?

It is not the end of the world if you pull the screw all the way out. You will have just earned the right to knock out the barrel retaining pins and pry the barrel out of the stock in order to put the screw back through the ramrod retaining spring. (The first time you do it, it is a real bear of a job and you have to be very careful not to crack the stock. Putting some oil on the barrel makes it much easier in the future.)

Anyway I would give those things a try. Please let us know how it works out. That is a great rifle you have there.

~Robert