The only thing I have heard of would be the military Bell of Arms.
It was a wood post with a round disk near the top that had notches to lean the soldiers muskets into. It then had a canvas cover to wrap around it. When in formal camp, the soldiers would stack their muskets in against that post, wrap the specially made canvas cover around it, lace/button it up, and stake it out tight. This kept their muskets protected from the weather and farily easily accessible.
A search of the Rev War sites for a Bell-of-Arms should lead you to some pictures/descriptions.
There probably were some fancy gentlemen's shooting accessories that could function like that, but I have not done any research on them.
It is one of those modern reenactment problems in search of a solution. Which is why various people have come up with those forged stands to stick in the ground, with a C shaped "holder" on top - often then wrapped in leather to protect the gun barrel. I have used them, and even made one for a friend many years ago. The only other alternative is to lay your gun on the ground - not the best choice.
But I have only seen/heard of that Military Bell-of-Arms as a documented solution to the problem. Of course, it does not need to be used with the canvas cover. But it would require a little bigger/deeper hole in the ground. And notches for 6 to 8 muskets - the typical "mess group" was 6 to 8 soldiers.
Just my humble thoughts to share, and best used in conjunction with your own research.
Mikey - that grumpy ol' German blacksmith out in the Hinterlands
