Hello Swampthing (great handle!),
223 Rem is an excellent caliber for 14"-15" inch Contenders/Encores. Many have also had great luck with the 10" barrels, but it may take a little more work to find a good load or handload. I have a 15" tapered factory Encore barrel in 223 Rem and it's one of my favorite guns, but it took some work to find the right load techniques. If you are interested in using indexing during your handloading process, PM me and I can help with that.
It is possible that with the right loads you can consistently shoot sub-.5" five shot groups at 100 yards with proper handloads for a 223 Rem. I do it even with a factory tapered barrel and I'm a terrible shot. You can do it too with a little work.
If you don't reload, you can still get good performance if you shoot several types of ammunition until you find the type your barrel likes best. I never did find a factory load my gun would shoot so reloading is my only option.
Safe and good shooting to you!
Javelina