"Early reports had the muzzle wedges and filler (which appears to be a metalized epoxy) falling out and now more serious problems of ribs coming off"
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I am skeptical, though, I suppose, it could have happened. Personally, I have taken the ribs completely off, and removed the muzzle regulation wedge too, on two different Sabatti doubles, one a .450/.400, and the second a .450 NE, and re-regulated them, by installing a mid point regulation wedge, and a longer muzzle wedge, so I know how those two examples were put together, using normal soft solder as commonly used by double rifle makers from day one, no epoxy, etc. Many others I have examined carefully, and I found no epoxy,metalized or otherwise.