I've owned a half dozen #1's (2 now) that have all been solid MOA guns. A couple #3's in the past shot pretty good too, both .30-40's and both only shot with mid-range cast loads. Used to shoot CBA competition with the one.
Issue is probably with the forearm. Have you tried it with the forearm completely removed? If so, and accuracy improves, then try hanger tensioning tricks and look at the inletting and if it binds against receiver (it mustn't).
Light barreled single shots are particularly prone to accuracy issues if there's contact at the receiver. I always fit them so there's a hair of light that shines through the gap, but still look tight.
