Ian Skennerton's book,The British Service Lee is a bit of a bible for info.He said the smaller lug would often give way if wet ammunition was fired often enough but I think the action is stretchier rather than a time bomb.
There is a YT clip of a 300 win mag chambered no4 being fired and this happens.
https://m.youtube.com/watch?v=7bhWxFbYdyw
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