The RCBS 9MM-124-RN is my bullet of choice for my "FrankenColt" (a whole 'nuther topic),.38 Super Combat Commander circa 1970.
I am currently shooting up all my NRA formula 50/50 Alox-Beeswax ammo that I have for it and intend on only shooting powder coated bullets in it from now on. So, I am also seeking to update my loads. I have been shooting relatively mild loads in the gun inasmuch as my handloading philosophy has always been one of moderation and safety. However, inasmuch as a .38 Super was intended to be a hotter number (than a 9MM), and inasmuch as it has a fully supported barrel, I intend on going for a little more performance, A.K.A., "velocity", than for moderation in this particular gun only.
Therein lies the rub...there is very little published data specific to my bullet (my finished bullets weigh 130-132 grains ...I usually extrapolate using other listed data for other bullets , of choice (please do not suggest a different bullet/mould), other than the old RCBS Cast Bullet Manual number 1. It shows only eight powders, all of which were introduced before 1986 and then one of those (Winchester 630), has been discontinued.
I have found that 3N 37 has shown to be accurate in my Combat Commander using jacketed 125 grain hollow point bullets and shows promise with my RCBS bullet. But I have to do some long distance driving to obtain any of that.
It appears that extrapolation using data specific to other bullet data will likely be necessary. In that vein, Power Pistol looks good via the latest Lyman manuals.
I would like others who specifically have used the RCBS 9MM-124-RN bullet in the .38 Super (1911 type autos, not revolvers please), to chime in here and let me know what kind of results you have gotten and which of the modern powders like Power Pistol, Silhouette, etc., show the most promise.