personally, i don't think a "ballistic coefficient" ever killed anything all by itself. and, i find all the emphasis upon ballistic coefficient bordering on occult enthusiasm ridiculous in the extreme. a good cartridge balances many factors, b.c. being but one among them.
end of the discussion, as far as i am concerned.
but, for those of you who simply must have an "intermediate infantry round" in 6.5mm, or .264 caliber, may i offer the following suggestion, along with the rather gratuitous observation that it would just beat the living snot out of the 6.5 grendel. (yes, you may infer that i regard most of the rhetoric surrounding the grendel as promoter's hype, and not much more. it's an o.k. round, even a good round, but it is not by any means superlative or superior.)
i give you the 6.5x55mm swedish, a very nice little round in its own right. i know i wouldn't want to be shot with one, at any distance.
it has a case 55 mm's long, and the specimen i just measured mike's out at 2.155" in length.
it is 1.726" long to the very well defined shoulder.
if you took the simple expedient of moving that shoulder back to 1.300", as i have done with the "jj's brit" using the .308/.30-06 family of case for fabrication, you will end up with a case somewhere in the neighborhood of 1.729" length. to do so, you will have to move the shoulder back about 0.426", by my measurement. (2.155" minus 0.426 ='s 1.729.)
i have trimmed my little "brit" back to 1.710" in case length, and trim a couple more thousands when i reload cartridges, to account for any lengthening of the case upon firing. i don't trim any more than that, because my little brit is so stout it doesn't stretch much after the first firing, if any at all.
if it is important to you that someday you wish to stuff your creation into an ar-15 magazine/magazine well, you could trim your case accordingly, or just leave it at 1.729".
it's up to you.
i think you would have a very nicely balanced little round. in fact, i may building one myself, and i think that i would call it "jj's swede," ™ in another spate of modesty. laughing. i'll assert trademark protection on "jj's .264 swede" ™ & "jj's swede" ™right now, and build one.*** with bullets in the 100 to 110 grain range, it will be a nice effective round.
and, as noted, i think that it would beat the socks off the 6.5 grendel. and quiet the clamor from that crowd, which would be an almost priceless side benefit. and, in an ar-15 if would outperform a grendel, and in a bolt action rifle with the bullet seated farther out, it would smoke the grendel. sort of the difference between the swede as made originally, and the carcano & mannlicher shoenauer & 6.5mm japanese, and a whole host of european 6.5's. incidentally, they are all long gone now, simply because the 7mm and .30 caliber weapons proved superior.
i will continue along with "jj's .284 brit" ™ for that very reason, e.g., the 7mm bore is just a superior stopper compared to the 6.5mm's. maybe not a superior target round, though it won't give away much on that score to the 6.5's either, but just a better stopper. so all the militaries of the world who have looked into it have decided, after experience on the battlefield w/ the 6.5's forced them to consider the move to larger rounds.
but, "jj's swede" ™ would make a decent round.
john jay @ 05.22.2012
*** anyone have a used barrel in 6.5mm you could sell me ridiculously cheap. and, any spare rifles in a short action you might give me, to support my intellectual and engineering endeavors & bent. i am a little short of the "vigorish" right now, and could use any charitable contribution you might spare. laughing.