There's a whole bunch of things, which, linked together, translate to accuracy. Start with the fact that,in a vacuum), short fat bullets spinning at low rpm are more likely to arrive in the same hole than are long, pointy bullets spinning a lot faster. The 6PPC,which is a modified 220 Russian necked to 6mm) has enough case capacity to drive short, 60-70 grain bullets to their optimal velocity,at least what we think is optimal). The 6BR can do the same--but will use more powder in so doing. So right now, if we presume the short bullets are more accurate,at least at 100 yards), there is no need for the bigger 6BR case.
That said, I do think, at 200 yards, in windy conditions, a 6BR with turned necks and, say, 90gr bullets, could possibly out-Agg a 6PPC. The PPC wprobably still have the smallest group I suspect, but the 6BR might have the smallest average of 5 targets. Until someone actually tries a 10- or 8-twist 6BR in "point-blank" competition, however, this is all conjecture. Two years back, Jackie Schmidt ran an 8-twist 6BR railgun for a test we did. With Berger 105s moving nearly 3000 fps, he shot an honest 5x5 agg of .185 or so at 200 yards. That means the average of five measured groups was,2 x.185) or .370".,Benchresters divide their 200-yard groups by two). So the .185 Agg means the groups averaged .370 center to center. That Agg would have won many BR matches, including the recent NBRSA Nationals in Phoenix.
Lester Bruno is doing some experimentation with a 6BR railgun. One reason shooters are not trying the 6BR in a 10.5-lb bag gun is that any time you go to more powder and heavier bullets you end up with more recoil and more "jumpy" movement on the bags. Recoil and jump can harm accuracy, so thus far the 6BR-fast twist option has not been attractive for short-range benchrest.
Looking at the conditions in Phoenix and the measured groups at 200 yards, I predict, within a few years, someone shooting a 6BR or Dasher,or maybe even a 6XC) with heavy bullets will manage a Top Five finish in a 200-yard stage of a short-range BR match.,This presumes that someone will actually have the moxie to try something NEW.)
Does that seem far-fetched? Well consider that a 105gr VLD going 3050 fps will have roughly HALF the wind drift of a 68-grainer moving at 3300 fps. That's a pretty big "head start" out of the gate. In switchy, windy conditions, if the trigger-puller doesn't make perfect wind calls on every shot, the heavier bullet might retain an edge when all is said and done.
10 mph crosswind,90 degree wind drift) at 200 yards
6PPC,68gr bullet, 3300 fps): 4.01"
6 Dasher,105gr bullet, 3050 fps): 2.12"
Still, an 8-twist 6BR/Dasher has not been used successfully in short-range BR competition... to my knowledge. But keep in mind that the 30BR with 110-120 bullets is the dominant cartridge in Benchrest for score competition.,But that's a different game and the larger bullet diameter offers it's own distinct advantage in score shooting.)
At the local club level in "fun shoots", fast-twist 6BRs have actually been pretty competitive at both 100 and 200 yards. At my local club, the record for a 100-yard, 10-bull score shoot was set in 2007 by a 6BR shooting Berger 105s.
WD
