The world lost one of the most knowledgeable antique and collectable gun guys on the 4th of July - about six years ago - to a Winchester-Lee. Glenn DeRuiter, manager at SARCO, was shooting a Winchester-Lee and the bolt blew back and imbedded in his forehead. I heard that it was case failure that caused the bolt to fail.
I remember reading an eye witness account of the accident (which I have been unable to locate) who stated that among the debris on the bench was a badly deformed cartridge case which evidently had been fired in the rifle prior to the accident. This leads me to suspect that the cause of the accident was insufficient neck clearance, which can prevent the bullet from exiting the case and cause a virtual detonation. This could be caused by failing to check neck thickness on formed cases. The mystery is why someone would continue to fire after experiencing such obvious pressure indications.
I also remember reading that Winchester used a Lee Navy action rebarrelled to .220 Swift to test fire .220 Swift ammunition, which would seem to indicate that at least the factory consideered it an adequately strong action.
At any rate, here is my Lee Navy sporter, which I expect I will be selling before too long, if any interest is shown.