Re: to build or to buy???
I'm not convinced anymore, that the 7 mag can do anything the 270 WSM can't. What you get from the 7 mag is 10 more grains of bullet weight. Other than that you can match bullet speeds and BC's. I shoot 180 gr Berger VLD's in my 7 mag at 2980 with a 28" barrel. Use the same 9 twist barrel for the Wizzum and you're shooting the 165 gr Matrix VLD with speed and BC close enough to negate any difference. Same thing with the 150 gr .277 vs 160 gr .284.
My $.02, for what it's worth.