Kirby, The 6.5AX certainly looks impressive, and its release comes at a time when I have been seriously looking at case possibilities for the Krieger 26 inch, 3 contour, 1 in 7 twist 25 cal barrel that I ordered last week. Also, my latest order from Richard includes 125, 130, and 156 grain bullets, and is due to arrive here in Oz in 2 weeks. (Already have some 142)
I have been looking for a rimless case that could provide a case capacity in the 85 - 95 grain range, and is capable of working through a magazine. Hoping to achieve 3250 - 3300 with the 142 grain bullet, and about 3100+ with the 156 grain bullet.
I had been looking at the 6.5m x68mm, 7mm Dakota, 7mm RUM, and even considered the rebated .425 Westley Richards. The 7mm Dakota seemed the best of those options, as it appeared to involve just necking down to .257 without any fireforming or shortening.
This is not meant as a criticism, but I note that you are using the 300 Dakota case, rather than the 7mm Dakota, and wondered what advantages the 300 Dakota case would have offered over the 7mm Dakota. I realise that the 300 Dakota with the .050 extra length would have about 5 - 7 grains (maybe more) extra capacity, but the 7mm Dakota would have been 1 less step in necking down to 6.5 or .257, and also a bit more friendly with magazine length, when using the longest bullets.
I guess that I am a convert to the longer neck design, but the 7mm Dakota has a .333 neck against .310 on the 300 Dakota, and a shoulder angle of 30 degrees against 32 for the 300. It appears from the graphic, that the shoulder of the 300 Dakota has been pushed forward and the neck shortened slightly.
One of the constant criticisms of the Dakota cartridges is the cost of brass, and naturally wondered whether this is likely to continue, or can we expect some relief from current prices in the future.
I commend you on the current initiative and also in the courage you have shown in developing new cases that you believe will benefit the smaller but nonetheless important niche market of long range shooters. I hope that this project succeeds, and at times like this wish I lived in the US, so I could access your services. Good luck, Brian.