IME Encores are pissy with rimless cartridges. Sounds like your problem is getting the case past the belt and engaging the extractor in the rim recess which is smaller than the belt ?
The design is like that used for rimmed cartridges, not positive like a Ruger No. 1. My 280 AI is so bad, I'm gonna convert it to rimmed by using 7x65R cases. I had a HighWall (original design) in 300 H&H that was also a PIA. Fixed it by converting to 300 Flanged (a rimmed, beltless 300 H&H). You could do the same as the flanged base is as big as the belt. You need to find a Smith with access to a reamer that will open up the chamber and then go thru brass forming.
Plan B would be to sell them off and buy a more appropriate chambering for where you hunt.
