Successful flight of my LOC Precision Caliber ISP to 1286 feet at 197MPH. Note the “pop” at the end of the burn, in person this was more like a shotgun blast, was visceral.
Strongly suspect it was the casting tube of the aft propellant grain being consumed and then spit through the nozzle. Have had this happen on other H250s. The nozzle looked just fine after and the altitude was “within the noise” of the sim and previous flights.