Re: 270 Dakota
Like was mentioned, a 270 AM is a 7RUM necked down. A 277 AM is a 338LM improved and necked down to .277. I think Kirby has his own version of the 270 Dakota improved to his AMish dimensions called a 270 AXM (Allen Xpress Mag) iirc.
That is the one like the 270 Dakota, and it has peaked my interest too; however, price and consitency of the brass has slowed me from looking into that round. Lapua was rumored to be taking over manufacture of the Dakota brass. If they do, it will still be expensive, but more likely worth the added cost to get such quality brass. On another note, it would allow you to push the charges a little higher and maintain the integrity of the brass if Lapua made it.