Take the stock off the gun by removing the recoil pad and stock bolt. Spray gun scrubber into the action and trigger. I use an air gun to blow the cleaner out then spray again. Before putting back together, spray with a light coating of lubricant, I use G 96. Gun should work now. Tom
If you have an XT with the adjustable trigger and it's NOT positioned all the way back, try moving the trigger toward you about half the distance between two adjacent dots and see if that helps. Tightening the pointed set screw where there is no dot will make a nice little dimple in the carrier to hold the trigger in place. I like to be able to comfortably position the trigger in my end finger joint.
If your finger is too straight before the pull you may not fully release it afterward.
That's a good thread but the OP states that the problem occurs regardless of which barrel he fires first. That rather eliminates a firing pin problem. Assuming that the shells he using recoil hard enough to set the triggers and that he is holding the gun into his shoulder firmly enough to direct most of the recoil into the action, it sound like something is preventing the inertia block from moving completely. Could be dirt, could be riding the trigger. I'd try the trigger adjustment before I ripped the gun apart.
I had the same problem, turned out that the inertia block had a small burr on it so it wouldn't set right. Took it to a gunsmith and he fixed it right up. I have probably shot 2000 doubles since without even the slightest recurrence.
Sometimes the spring on the inertial block is too stiff for the loads you are shooting, especially if you do not mount snug to your shoulder. A gunsmith can grind down or replace the spring with a lighter one and solve the problem. I just had to grind the spring down in my new (old) Win. 101 Pigeon Grade, because I shoot light loads.
In any case, it sounds like something is keeping the inertial block from moving far enough. It can be as simple as powder residue building up.
The inertia block has to go under the hammer sear to lift it to fire. With stock off fire the first shot trigger, gun empty o0f course, slade the inertia block back by hand, then pull the trigger again it should drop the hammer if not, the inertia block sear part that lifts to for the bottom or top Bbl nedds a very light file jod so it goes under the sear by about.0005.
This should correct the problem, also are you holding the gun formly to your shoulder? so the inertia block works properly, also lube the inertia block w/Rem Oil.
There are a spring and plunger in the trigger which returns the inertia block to position. You can get dirt build up or in some other way restrict movement of the plunger and the inertia block will not return. You can see the position of the plunger from the rear of the trigger and see when it does not return properly.
with the stock off, flush it thoroughly. You may even have to take the mechanism apart, but the plunger sticking will cause the gun to fail to fire on the second barrel regardless whether the upper or lower barrel is fired first.