I’m with Bob on this. I went through the list in my brain and couldn’t come up with anything. Are there any markings whatsoever?There are many dozens of tripods for early MGs that one only can see in the "Weapons Mounts for Secondary Armament"volume and I can't find it tin there.
This tripod has a rear mount so most of the above suggestions are disqualified. The groove on the inside of the clamp suggest a gun with a circular ridge around the jacket for the clamp just like a Lewis, but the Lewis does not have a rear mount. Jap Naval Lewis has a tripod but not like this and both Brit and US made special Lewis adaptors for Vickers and US tripods.
Or the groove might be for a leather strip, etc. The clamp appears larger than a Lewis anyway, but might fit a smooth jacket Vickers or BMG.
Could fit a Browning watercooled as well, but the length of the cradle looks a bit short. The head of the rear mount pin has somewhat of a Browning 1917a1 rear pin look to it.
My notion is that this one might be for one of the early watercooled MGs invented and built as prototypes in early 20th century but could not compete with the dominant types. Very interesting and quality built tripod.
FWIW
I believe you are correctLooks like a recoilless rifle tripod. I suggest measuring the interior diameter of the front mount, metric and inch, to get a rough idea of size to inform your research.
Shannon
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