Your not missing anything. The guys seeing the big delta are typically using the wrong powder in the 6BR, as a comparison, the new 6BR(BE) when correctly loaded is being called the
6BR-BE, pronounced
6-burbee, (the 6 BR bra eater,) 30" bbl, 105g burgers, 3000fps, all day, every day at least here in earth quake, fire and indigent illegal aliens country. Works exceptionally well in F and long bench where the longer bbls are used. all the short barrel events, the 6.5x47 with a 130ish bullet is probably better.
Some of the fellows i talk to just cant seem to get the same results in certain parts of the county, who knows what the real root causes are, there are many variables rifle and chamber to chamber design, regional atmospherics.
The BRA thing is a current poster child made famous on the internet by a few famous shooters that would and have done well with any of the equivalent cartridge designs. I-net marketing at its best. Arguably the chamber design for a 6BR to really shine and perform does need to be correct. In my case it took a bit to get the design right and of course is proprietary except for a few, but its worth your time and energy to pursue the reamer designs not the morphed case designs.
Or not.
Enough of a break and time wasting exercise, i need to go finish clambering another
6 burbee.
Blinded by the light,,,,,,,