Welcome to HHM!

As Ernie first mentioned, the .223 barrel is a must, IMO.

As Rod touched on, if you want to supercharge your Contender, consider the JDJ line of cartridges. It has oft been said that if you own the 6.5 JDJ and .375 JDJ barrels, you can hunt anything up to and including elephant.

And then just for the heck of it, throw in a .309 JDJ which gives the .308 a run for the money.

And I agree with karl, the .17 HMR is incredibly accurate and a real rocket for small varmints!