In my experience Trevor, (I've shot an open gun a couple of times) you can typically build a load around the gun and how it is set up- comp etc.... Short comps, with few chambers can get by with some slightly faster powders. Long multiple chamber comps can make use of lots of slower powder, which is what I prefer. Comps with barrel ports, well this thread can get long really fast, but realistically I would look up some tried and proven loads and experiment with what feels best. You might be able to put up with muzzle flip if the recoil is soft, or maybe you can tolerate hard recoil, if the gun stays flat. If I seen a pic of your gun and see the comp I may be able to recommend a few things to try. Big comps with lots of chambers have lots of baffle surface for the muzzle gasses to slam against pulling forward, and chambers allowing the gas to be redirected upwards to aid in keeping the muzzle down. Pats links are good ones, you will likely get lots of feedback, but if it was me that just bought a used gun ready to go, I would experiment with loads until I found one that felt good, was accurate and also with powder that I can get my hands on. Hope you find one that works for you! To get started, .38 Super with say 2-3 chambers, 124gr bullet, I would try IMR 7625. Large 3 chamber comp and larger, 4-5 chambers etc... with or without barrel ports in .38S I would consider IMR 4756. There are lots of powders and combinations out there, go on the enos forums, there is lots of data on there as well. I like the Hodgdon brand, and use HS6 and Longshot.