We describe our ongoing work to develop a new medium-energy gamma-ray Compton telescope using advanced scintillator materials combined with silicon photomultiplier readouts and fly it on a scientific balloon. There is a need in high-energy astronomy for a medium-energy gamma-ray mission covering the energy range from approximately 0.4 - 20 MeV to follow the success of the COMPTEL instrument on CGRO. We believe that directly building on the legacy of COMPTEL, using fast scintillators that improve the response while preserving time-of-flight background rejection, is the most promising path for such a mission. Fortunately, high-performance scintillators, such as Cerium Bromide (CeBr3) and p-terphenyl, and compact readout devices, such as silicon photomultipliers (SiPMs), are already commercially available and capable of meeting this need. We are now constructing an Advanced Scintillator Compton Telescope (ASCOT) with SiPM readout, with the goal of imaging the Crab Nebula at MeV energies during a high-altitude balloon flight. The balloon payload is scheduled to fly from Palestine, TX, in June 2018. We describe the complete instrument and payload and present the latest calibration and simulations results. We expect a ~4.5-sigma detection of the Crab in the 0.2 - 2 MeV band in a single transit. If successful, this project will demonstrate that the energy, timing, and position resolution of this technology are sufficient to achieve an order of magnitude improvement in sensitivity in the mediumenergy gamma-ray band, were it to be applied to a ~1 cubic meter instrument on a long-duration balloon or Explorer platform.