June 18, 2021 Update:
Work proceeds on the root cellar: This week I built the forms so I can start pouring concrete for the foundation. 

I also made a bit of a breakthrough on my pistol sabot project.  For some time, I had been seeing sporadic performance of the saboted rounds: sometimes they would work well, other times the accuracy would spontaneously degenerate by a factor of ten.  For a while, my hypothesis was that the base was shearing off or otherwise failing, but making the base thicker didn't provide any improvement in reliability.  Finally, it occurred to me that maybe gas was leaking around the base and blowing the petals off the sabot while it was still in the barrel.  I redesigned the base of the sabot to try and reduce the potential for gas leakage, and the first test batch showed a huge improvement in reliability.