By Norm Johnson
The below may give you a clue. My experience was with a Contender but the principles are the same with the Encore.
Cases shortened (talking shoulder set-back here, not overall case length) in the gun are a result of pressures not being great enough to cause sufficient case obturation. The firing pin blow is strong enough to set the shoulder back some. A friend has a .35 Remington that will demonstrate this characteristic to such a degree that after only one firing of a light load, head space clearance is so excessive that subsequent reloads will not fire.
I actually learned how to solve the problem when I had a similar problem with the 7 TCU, my first Contender experience in 1981. I found that with my particular chamber/die dimensional relationship that I was getting (infrequent but aggravating) failures to fire. I suspected the shoulder setback problem so I loaded some bullets long so that they would be forced into the rifling when chambered. Long seating of the bullet is a little more critical with an action like that of the Contender because it has no camming action as does a bolt gun. Anyway, I used this method to blow out the shoulders with 100% success.
I then smoked a case and set my resizing die to resize only about 90-95% of the neck length. Viola! All cases that had been blow out fired normally. I had again proven myself the great problem solver!
But wait!
After 3 or 4 more reloads of those cases I started experiencing more failures to fire - only now the failures occurred 3-4 times more than the they did before my magic touch.
Careful examination of a chambered case hinted that the reloads that failed to fire were just a tad long, that is, their case bases were a few thousands above the breach face. Since I knew it was not the bullet being seated long, I surmised that the case had lengthened just enough that the Contender would not lock up properly. The action would seem to close ok, and the hammer would fall leaving a faint firing pin mark, but it would not fire.
So I took a case that had failed to fire and, tweaked the sizing die down just a hair at a time (1/32 turn) until the case base appeared to be just flush with the breach face when chambered. I then ran a few reloads to test my efforts and all was well so I locked the die in that position and resized the rest of my cases. To the best of memory, I have had no further misfires.
The unusual characteristic of the Contender being able to apparently lock up but not fire must be mystifying to lots of reloaders. It certainly was to me! Some years later one of the gun writers did an article on the same problem so it is not unique to my gun.