Welcome to the forum. Basic rules are to join in, have fun, and play nicely with the rest of us kids.
Not sure what you are asking? 5.56 NATO and .223 cartridges are the same size when new, since .223 is just the commercial version of the round which was originally developed for the military. The 5.56 NATO chamber is a little bigger and has a longer freebore than the commercial chamber, so pressures will run a percent or two lower in the NATO chambers but not enough to cause concern. The reason for those larger dimensions are to ensure good feeding in self-loading and particularly in full-auto weapons and also to accommodate specialty ammunition that would jam in the throat of a commercial chamber. I have yet to run into any specialty ammo that won't fit in a commercial .223 chamber, but that doesn't mean it's not out there.
If you use a commercial chamber, as in your Encore, just check that your NATO round doesn't jam in the throat, leaving rifling marks on the bullet. If not, it should be good to go. You can check by coloring the bullet with Magic Marker, chambering and removing it without firing to look for rifling marks on the bullet near where it meets the case mouth.
There SAAMI spec Piezo transducer pressure limit for .223 in psi is lower than the NATO spec for 5.56 NATO, but the older copper crusher unit limits for both are about the same. The European CIP does not give any pressure difference in its limits for the two rounds. AFAIK, both are therefore safe in either chamber except any long NATO specialty rounds you might encounter, as I described above.
