Listened to the S2H video tonight, comparing the capacity of 6prc to 6um30, I believe once the um30 is formed there will be a notable increase in capacity. I know fired (not sized) adg 65prc VS 65saum is a 69.X VS 73.X when I weighed them with water a few years ago. 6um30 has the shoulder just a touch longer, so it'd have the slightest more capacity when comparing the 2 different 6.5 versions. The biggest advtage of going Saum parent VS prc, is that extra 4gr more room, allows you to stuff in 3.5 more grains N570. This allows you to get to pressure with this powder. The standard 6prc(in my 20in) was 12" drop tube full case at 61.5gr and just got the slightest powder crunch with a dtac, it was running 3130fps. Rl26 out performed it in the prc variant. My 6saum is a 24" and 66gr N570 was running the dtac at 3460. I have an 8tw lt palma 6groove ace blank getting cut at 20in in 6saum currently. So I'll have a more consistent comparison, however the prc is running a 4gr 7.5tw. Which in theory should build more pressure than the 8tw 6 groove.