It could be that the previous owner/s had taken the for-end off with the hammers let down, and upon putting the for-end back on they used it to re-cock the hammers and reset the ejctors putting a lot of tension on the wood and metal. It could be that the thin areas of the for-end that fit over the knuckle of the receiver are slightly bent even though they are case hardened. Are there any chips out of the thin areas to indicate this?

David