Thanks for the replies. The previous owner had loaded it and then put it in a locked gun cabinet. He decided he didn't want to hunt anymore, and gave it to me recently. He is of sound mind, so when he says it's 90 gr. of BH, I don't doubt him. Bore is clean (looked with a light).
Edit: I know how to remove the breech plug, and can push it through. I didn't know how stable BH was with age.