Yep..... a 2-1/2 year old thread (maybe you missed that aspect).
Bryan has moved this subject on a bit since 2015 as can be seen in his latest 'Modern Advancements' books with mentions of tests using super-twists for ELR shooting. Since this thread started up, the whole issue of the relationships between stability, rotational rate, bullet shape has been explored further with the King of Two Miles challenge and other ELR exploits having come along.
That raises questions (in my mind at any rate) that whilst there may be benefits to stability in trans / sub-sonic flight modes from some or all of these changes what effects do they have on more 'normal' long-range shooting, with less exotic cartridges / bullets than seen in KO2M etc - that is up 1,200 yards or so? Are there benefits waiting for us F-Class and FTR shooters who don't exceed 1,000 yard distances? Or are such changes precision neutral at these shorter distances? Or are they of benefit at ELR only and have downsides at distances where the bullet is still comfortably supersonic?
I'm still intrigued as to how come the old 155gn Sierra MK, the 2155 version works so well at 1,000 yards in GB 'Target Rifle'. At 2,925 fps MV with an average 2.14 G7 BC, it cannot stay above transonic speeds at this distance. At 1,000 yards it's predicted to arrive at the target doing 1,151 fps in what would be a nice day in the Bisley 'Imperial Meeting' - ie ~70-deg F in this relatively low lying range. Say it outperforms its specification and actually produces 3,000 fps MV, it still drops to a shade under 1,200 fps at this distance. Last year's 'Imperial' was shot in warm (by English standards) and mostly light winds and the scores were uniformly high at all distances including at 900 and 1,000 yards - lots of 'possibles' with just an occasional dropped 'V'. Increase the ambient temperature to 85-deg F which a few matches might have been shot in and with 3,000 fps MV the bullet is predicted to be right on the old US Army key boundary of sound barrier + 100 fps. With 13-inch twist barrels the norm, the Sg is comfortably high, but not in the super-high levels that Bryan is now talking about in Modern Advancements in Long Range Shooting. This also assumes that there is a nil MV spread - at normal temperatures, certainly in winter ones, the slower bullets risk being subsonic rather than seriously transonic.
This is of purely academic interest to me as I haven't shot 'Target Rifle' for a long, long time and never came anywhere near doing so well enough to consider entering the 'Imperial Meeting' anyway. I just wonder that as these guys and girls are doing much better than theory and practice says that they should be doing, whether there are issues that effect those of us who shoot long-range precision disciplines such as BR and F.
The one certain thing is that most of us know a great deal more today about these issues than we did 10 years ago. (In year one of FTR, the experts were telling us to shoot 155s in 308s and to use as slow a twist as possible - my first FTR barrel was a 13.5-inch twist - bad move for shooting the 155 Lapua Scenar at 1,000 in chilly November European F-Class Championship stages! My second barrel which came not a lot later was a 10!) And we have to thank Bryan for in my case anyway about 99% of that increased knowledge of what makes long-range rifles and bullets work, or not, as the case may be.
