303 barrels are available from Ron Smith and Bevan King in Canada (not sure if Bevan is still active). They are available from Shilen, McGowan, MRC, Krieger and probably some others in the States.
The last Sierra match bullets I got were over sized at .3116 and didn't shoot well in my rifle. In fact, the Speer 180 grain RN bullets shoot better. I will probably rebarrel to 30/40 Krag just due to bullet availability. The 303 barrel will get turned down and installed on a sporter. Regards, Bill.