My local club had a member (President at one point) that was a big BP cluster guy. It was way before my time and you know how stories change over various re-tellings, but he was a 'flash in the pan' guy and lit a lot of motors. I don't think anything like 312 as mentioned above, but the rockets were supposedly 6-8" diameter and supposedly had a bunch of motors (100+).
I did meet him one time and I know other club members knew him well and could give more accurate information for sure, but it sounds like in the 80's/90's, there was some very interesting stuff happening with big clusters and as time moved forward, it might have become significantly less desirable due to how things were being done vs. safety. Again, never saw any of it, but might have liked to see it at least once. . .
My personal biggest was a 6->3->3 24mm 3-stage rocket a friend of mine and I built called the 3 Stooges, bottom stage ignition using Quest Q2G2 igniters at the time, but would easily fly it again with homemade or augmented Estes igniters if we wanted to, as we're low on Q2G2's. It was not cheap to fly. I cant imagine the mega clusters. . .
Sandy.