In my experiance, and I mean EXPERIANCE, not "I've heard". Shortening a 6BR takes away from its strength. It is not a good choice for Short Range BR!
The same can be said about the 6PPC, it is not a good choice for Bench Rest beyond 300 yards!
This not a guess, I built my first Tall Dog about 30 years ago, have been shooting BEnch Rest from 100 to 600 yards for longer than that. It is not just me, many have found the same thing. If they can win with another cartridge in short range, they all win more often with a PPC, just a proven fact.
Like a 30BR, probably the best competition for the 6PPC. At a 100 yards it might rule, but crank the wind up, and on an average, it becomes to hard to steer compared to the 6PPC. Most days in the end, the grand agg is going to the 6PPC, and at the end of the match, that's what it takes to be a winner.
Score may be different, as absolute accuracy, is now over ruled by the best outside diameter. I shoot very little score so I won't comment where I don't have enough experiance.