DavidF: Yes I am using green sand (silica sand mixed with 5% bentonite). Finally, it succeeded using a dirty hack: I tilted the mold 30 degrees to it had more hydrostatic pressure and it filled the mold completely. However, the side effect is that opposite of the gate (at 7 to 8 o'clock on the sundial) the casting is rough. On top there was probably also a bit too much upward pressure, hence it leaked a bit out. At the bottom I clamped the cope and drag together. The temperature was no problem, it was blindingly hot, it was nice fluid when stirring with with a steel bar and the infrared pyrometer showed 1430 C (2600 F) and outside the crucible (the coldest spot opposite the burner entry) 1540 C (2800 F), but that is usually higher than the metal temperature. The pour also went quickly. Video: https://www.metallab.net/jwplayer/video.php?f=/clips/others/Iron cast 20201028.mp4 The mold: The final casting, between the sprue and casting it spilled between the cope and drag but not on the casting itself.
