Bought one (t3x 20" 6.5cm) this summer. I went straight to RL16 for my powder for the very technical reason that I had ~2lbs of it and nothing that I need to use it in. Put another way, there are other powders that would work; I used what I had.
20" Tikka, Peterson LRP brass with CCI LR BR primers, seated to 2.93"ish which put the 147eldm close to 0.060" off the lands which is where I like to try to stay. New brass, 42.3 grains of RL16 gave me 2610'. After the first firing, the now-1x fired brass with 42.0 gives me the same speed.
Based on what I see when I put this load into Gordon's Reloading Tool I believe that I could push it up to around 2650' velocity at safe pressure and that's what I saw early on when I pushed the powder charge a bit. I don't remember details, but I saw a faint ejector mark at a heavier charge that went 2660' IIRC.
I have also considered trying to switch to RL23. I think I could beat 2700' with that powder, but I am trying to hoard what I have for use elsewhere. 2600' is plenty for what I do with the rifle.
I don't have notes at my fingertips but ES/SD with new brass was something like 45 and 15; with 1x fired brass it has been maybe 25' and 10'. Point being, it tightened up with formed brass.
ETA: the only other loads I've shot have been the Nosler 123CC and the Hornady 130ELDM over 38.0 of IMR4895. I shot those just to have a gentle load for my eight year old's introduction to the rifle, and to burn up the handful of the 123s I had left over from a long-gone other project. I will likely use up the rest of the 130s with the same powder for practice ammo for the kids.
