Here's a GEM 40. I couldn't get the Isp to change but I noticed this is an issue with the Castor 4AXL which is supposed to have different Isp and weight than the Castor 4BXL but actually is identical except for prop load. This GEM has the correct weight and prop load (and is a little longer), but still has the Isp of the Castor 4BXL for some reason... +PART[KWsrbGlobeI]:FINAL { %RSSROConfig = true @name = RO_KWsrbGlobeIGEM @MODEL { @scale = 2.54, 2.656078, 2.54 } @title = GEM 40 @manufacturer = ATK @description = Graphite-Epoxy Motor (GEM) %mass = 1.4 @MODULE[ModuleEngines*] { %maxThrust = 499 %origMass = 1.4 @atmosphereCurve { @key,0 = 0 274 @key,1 = 1 245 } } !MODULE[ModuleGimbal] { } @MODULE[ModuleFuelTanks] { @volume = 6640 } @MODULE[ModuleEngineConfigs] { %configuration = GEM40 %origMass = 1.4 @CONFIG[Castor4BXL] { %name = GEM40 %maxThrust = 499 @atmosphereCurve { key = 0 274 key = 1 245 } } } }