You won't be able to rechamber the barrel you have. You can however pick up a 243 barrel from Midway that is fully chambered. You'll need the barrel, barrel nut wrench, barrel vise, head space gauges and an action wrench. You will also need to change the bolt head and most likely the magazine box and follower. By the time all is said and done it is cheaper to buy a gun chambered for the 243.