Another thing to try that may bring you happiness is granular filler. Pick a powder that you know is safe as a full case load, like 3031, 4064, 4895, etc. Now drop it back about 1cc and replace that with BPI shot buffer, Cream 'o' wheat, etc. so that you have a compressed load with the bullet seated. This trick has allowed me to shoot undersize bullets through a number of rifles and handguns with good results in the past.
I am surprised the BP loads didn't work. I shoot air cooled wheelweight bullets and BP all the time with good results. I would have used a real BP lube, but otherwise I would have thought it would have worked. Heck, paper patched BP loads use bullets PATCHED to bore diameter, so the actual bullet is way below that and they shoot really good once you develop a proper load.