Not sure of what was posted on the other site, but a quick easy way to tell if it is the locking bolts causing you problems is to take a black marker and ink the top of the bolts. Open and close the barrel several times and see where the ink wears off to. If it does not line out pretty much all of the half moon cutout, the bolts are not engaging far enough to fully rotate the butterfly. If the butterfly is not fully rotated it can drag on the hammer block as it drops and the block will not fully clear the hammer before it falls. You will still get the firing pin indentation, but it has not stuck hard enough to fire the round. Take a look at the wear mark on the locking bolts some of your barrels that do fire for a comparison. If that is it, it is simple with a fine flat stone to take a little off the tops of the bolts to make them engage properly. Secure your barrel and "feel" the stone so it does not rock on the bolts. Try to take an even stroke and try not to change the locking bolt angle. Re-ink and test after several strokes until you get the hang of it. You will not need to take off very much. It sounds more difficult than it really is. Worst that can happen if you fail, is that you will have to buy a new set of locking bolts (which you are looking at anyway) and new bolts are cheaper than the shipping to T/C.
FWIW Mike