If you have a Buffalo Newton rifle, I'd recommend that you have the rifle checked out by a gunsmith before you shoot it.
When Newton went into bankruptcy and was taken over by a bank, there was an effort by the bank to recover as much money as possible from the Newton company. Many rifles were assembled from parts lying around- some of which were lying around because they were rejects.
About 25 years ago I met an older fellow who's Dad had worked for Newton rifles in Buffalo. This fellow owned a Buffalo Newton he'd inherited. Unfortunately, the rifle he had was made with a barrel that had never been heat treated before assembly. The first shot bulged the chamber. I still have a 256 Newton case in my collection that this fellow gave me, with a large bulge just ahead of the extractor groove.
Ken Waters Pet Loads article on the 256 Newton is the only reliable source of load data I know of. There is some older data that surfaces occasionally, but, powders have changed, pressure testing methods have changed, etc, since then.
Barstool's link is a great one. That appears to be a second source of modern loading data.