Sierra 120 Tipped Gameking

[grayfox]

Comparing the 123 MK from JBM bullet length values to this new 120, seems the 120 tgk is about 0.012" longer, 1.295 and 1.307 (my measurement on the tgk). So, not considering if the boat tail dimensions throw us off or not, if you load the tgk a bit longer, say +0.012 (ie, 2.272 cp to Sierra's listed 2.260), you should be able to reference the Sierra load listings for that 123 as a guide. I'd expect the actual MVs to be 20-30 fps faster than the 123, but need to factor in any delta's from your barrel to the sierra test barrel.
Also haven't looked lately but I'll bet there is some load data for the 123 smk in the Grendel handbooks too.
So couple of resources there to consider.