I’m running this exact same setup.
Mixed cases,
RMR 124g FMJ RN bullets,
CCI 500 primers,
titegroup powder.
I’m shooting these out of my Glock 19, 17 and shield.
I started at 3.6gr and moved up from there. They all cycled fine but felt like powder puffs. Knowing I was at the low end I moved up gradually and now I’m at 3.9 gr and am happy with the results. My C.O.A.L. Is at 1.14”.
I have not put these over a chrono yet but I do have one on order and will hopefully test these next week. Depending on the results I’ll make some adjustments and probably seat the bullet deeper.