.266 is smack dab in the middle of .224 and .308, so there you have it. Creed, x55, or 6.5-06. Find a rifle you like in any of those and go forth and have your gap filled.
I seriously want nothing to do with a 243 or 25-06. My 22-250 will do anything a 243 will do, and for some reason I have no desire for 25 anything.
My gap between a 22-250 and 300 H&H is filled with a 6.5 Creed, a pile of 270's and a few 7-08's.
