I have been using Speciality Pistols for Hunting Whitetail Deer here in my native South Dakota since 1982. In the years since then I have used several different cartridges some of which have been mentioned here by others.
More to the point, since you mention you have an Encore, you'll be shooting Factory Ammo and that you want to be able to hunt Whitetail Deer and Varmints with this single Barrel I would personally recommend a 15" T/C Encore Barrel in .243 Winchester. A couple years a buddy of mine won our Shooters Club Raffle and choose a 15" .243 T/C Encore as what he wanted to get. At any rate the Encore arrived and he promptly dropped it off at my house and requested that I mount up a scope, test a few different factory rounds in it and if I had time to work up a good handload that he could use on both Whitetails and Varmints.
In regards to handloads I ended up loading 80gr. Speer Hot Core Spitzers to a muzzle velocity of 2920 FPS. It just so happens for the non handloader this very bullet is available in Factory Ammo from Federal (even though I do not know what velocity this factory load will produce out of a 15" .243).
At any rate after we broke the barrel in on my buddies Encore, found the load that we figured would best suit his needs he insisted I use his Encore to take a Whitetail since I had done all the work on the handgun. Well Jan 1st opening day of our special Antlerless Deer Season I used that very Encore Handgun with the 80gr. Speer Hot Core Spitzers in my Handloads to harvest 2 nice sized Whitetail Does. Both does were slightly over 200 yards when shot and I had a good rest to shoot from.
Upon the shot the first doe dropped in her tracks and never moved with a center chest shot. The bullet entered behind the nearside front shoulder, took out the lungs and exited behind the offside front shoulder leaving a quarter sized exit hole. Complete penetration.
After I shot the first doe the second doe sprinted a few yards and stopped. Again I was on a solid rest but just as I started my trigger squeaze the doe started walking. Yep I messed up and hit her to far back. At the shot she sprinted for almost a hundred yards and stopped under the branches of a russian olive tree. Well I was committed so I again got the Encore up on the rest and when everything was right (crosshairs midway top to bottom on her chest and right up tight behind the front shoulder) I touched the trigger. At the shot the doe dropped in her tracks. Yep I was right, I hit her too far back the first time, but the second shot was right on the money, and the results were much like the first doe. Entrance behind the near side shoulder, destroyed the lungs and exited behind the off side front shoulder leaving a quarter sized exit hole.
Now granted shooting two deer with a single cartridge or load or bullet doesn't prove much. However I have also used this same 80gr. Speer Hot Core Spitzer Bullet out of the 6mm-223 and 6mm T/CU in Contender Handguns over the years and the results have always been the s ame.
You stated you ordered a .223 Remington Barrel. I consider the .223 Remington a little small, but since it is legal in South Dakota to use for Whitetails, yes I have taken a few Whitetails with a 14" T/C Contender in .223 over the years. The one thing I learned quickly is that when some of these .22 Caliber bullets are slowed down as they are from the lessened muzzle velocity from Handguns vs Rifles they react very differently than when they impact something fired at rifle velocities. If it were me and a .223 Handgun was all I had to shoot at Whitetails I would opt for either a Handload or Black Hills Ammo with a 60gr. Nosler Partition Bullet.
Good luck with your quest for Handgunning Whitetails. It is a very addicting sport.
Larry
PS and oh buy the way, like has been stated earlier in other posts you will not have just one barrel for long.
