LOL. Cluster. What a cluster fluck.

Its a "cassette".

In any event, good test on the cranking. When you say it jammed between the RD and the largest cog on the cassette - you mean on the wheel side of the cog? Or the next smallest cog on the cassette? And when you un-jammed it - was the chain on the idler pulley/cog nearest the cassette? Or was it off of that idler as part of the jam?

Someone already pointed out the adjustable stop-screws on the RD mechanism. If the RD throws the chain too far "in" (towards the wheel/tire) it is possible the chain could ride up and over the teeth. That doesn't sound right to me, though, if everything was adjusted before and the only difference was the new chain.

I suspect there is something that is bent, or otherwise misaligned. I had that happen to me with my folding bike. I swapped the tires F/R earlier this season to balance the thread wear (will need to do that again soon - the small tires wear faster) and I managed to put some odd pressure on the RD maneuvering the wheel on and off. I had to reset the RD adjustment etc to get it dialed back in. Not much of a problem, but it was avoidable work if I was more careful with the taking out/installing of the wheel...