RE: blackhorned caused rust
First off remember, we take the oil out of the barrel before we shoot. We also pop 209 primers through the rifle. Then we shoot Black Horn 209 powder. Actually it does not surprise me at all that your rifle rusted. Three weeks without any cleaning or oil to protect the bore, IMO the rifle should have rusted.
While I like Black Horn 209 powder, I would never leave a rifle uncleaned. Even my center fire rifles get cleaned and oiled. When you shoot a rifle, you fowl a rifle. When a rifle is fowled it will rust. No matter what powder you shoot. Some just take longer then others. Its a shame you had to discover this the hard way, but it is a wake up call to all people shooting their rifles, no matter what powder. If you shoot it, you should clean it..