Re: 600 yd Fclass Cal 6BR vs 6Dasher vs 243 vs other 6
I've had a couple 6BRs and they are indeed tough to beat in 300/500/600yd matches.
My 6 Dasher has a *slight* edge... but if I ever get another one, I'll be damn sure getting a hydraulic forming die or a lot of COW for fire-forming cases. I did the neck-up to .25 cal, neck down enough to form a false shoulder, fire-form, then neck turn, routine. Neat for about 50 rds... starts sucking badly for 300+ rds.
The 6-6.5x47L I had was a friggin' laser. Mine was short throated by request, so it had slightly less boiler room than some might. It ran the same bullet (B105VLD) at the same speed (3070-3080fps) from a slightly shorter barrel (28" vs 31") with somewhat more powder (39.5gn H4350 vs. 33.2gn RE-15) as compared to my 6 Dasher. Way easier to form the cases - neck down and go shoot, and if there was any accuracy difference I couldn't tell it.
If F/TR is an option, a good .223 Rem w/ a 7" tw throated for 80s or 90s can be very competitive @ 600 and in.