I've got a chamber casting. (Just can't find my calipers, and am waiting for new ones from Amazon to arrive.) The casting looks exactly like the .257 Roberts drawing in Richard Lee's Modern Reloading, but the seller said that .257 Roberts wouldn't chamber.
What with one thing and another --the bullet part of the casting is miking approximately .257--, I think the inevitable conclusion is that the rifle is chambered for the old wildcat .257.
