Charles Lancaster made barrels that are smooth inside but is oval, just like a 2 groove barrel excepts but smooth inside. They look like they are woren out. These barrels were first used in muzzleloaders but Lancaster used them on center fire rifles also. I am not sure when they quite, my gun is a 1901 action but may not have been finished until 1902 or 3. It is in 375 2 1/2 nitro Some of the Quebec Ross sporters also used the Lancaster barrels according to what I have read. This is the only one I have seen but Ihave heard of a 303 and I see Rossguy has a couple, lucky guy
John