Two things are most assuredly in play here.
1. Headspacing of the TC Encore due to the frame/barrel gap. Go the Mike 'Bellm Website below and read on how to correct headspace.
Mike Bellm - Table of Contents
http://www.bellmtcs.com/store/index.php?cid=172
2. Your separation is caused probably by improper die adjustment also and creating too much headspace off the shoulder, forget the belt. Case separations are caused by pushing the shoulder back too much and when fired the case surges forward again, creating that line which separates. With a possible frame/barrel gap issue and and improper die adjustment creating too much headspace, that is causing your case separation.
Got to throw the BS flag on NS being a magic cure.
Neck sizing is touted as being the magic cure when the issue is improper FL die adjustment 99.9% of the time. the factory instructions do not help in this manner either. Most people bump the shoulders way to far back and that is what is happening here.
Plus NS only in an Encore due to frame stretch will lead to misfires.
NS only does not lengthen case life and no one has ever proven it. In reality the facts are just the opposite. Plus after 3-4 firings you have to bump the shoulders anyway or throw the case away unless you are shooting powder puff loads to begin with.
The world record 1k BR 5-shot group of 1.4 inches at 1k with perfect 50 score and 5x, was shot with 338 Lapua cases loaded 54 times and FL sized every time. The cases were finally thrown away after the 80 firings. NO NS only case has remotely equaled that.
If you have FL die that fits your chamber you will not have the problems.
http://www.bellmtcs.com/FAQ/adjusting_dies.htm
Plus belts or no belts, learning to set up the dies will solve the bump back problem. Learn how to headspace off the shoulder not the belt!
Learn how to measure case shoulders, set up the FL dies properly to do a shoulder bump of .0015-.002 and you will have zero issues and the cases will last as long or longer than anything else.
NS only is a poor substitute for learning how to set up dies correctly and that is all it is.
BH