I have a 264 Win mag that has a 27 3/4" Shilen barrel on it. That is all the length you could get out of a 28" blank. It is a screamer. 3350 fps with a 130 Nosler AB and Retumbo and perfect results on deer. I was getting over 3600 fps with 120 ballistic tips. I was afraid to use them on deer at that speed. Can you say evaporate on impact. Barrel length is your friend
. I picked this rifle up almost new from my buddy, less than 60 rounds through it when I got it. The 6.5-284 is a more efficient round, (less powder usage) and you can get Lapua brass for it. I would have it built on a long action and use an 8 twist barrel if you want to use heaver bullets and have all the case to work with.