Thinking out loud:
On your second barrel, you can't go wrong with either chambering.
All depends what you want it for.
I would go with an 1-8 for the 6.5 and 1-9 for the 7mm.
If you want to add the LR component in the 6.5-284 I would do a compromise throat for the 130 VLD-140 class of bullets.
Even if you just set it up for the 130 Berger you couldn't go wrong.
They are awesome all around bullet for pd's, steel through mule deer (not used them on elk, but I would though).
The 140-142 class bullets would be just seated a little deeper whic has not hurt accuracy for me.
If thinking LR some would want you to do compromise throat for the 284 Win from the 162 A-max to the 180 grain Berger/JLK.
In the 284 I would for myself throat it for the 162-168's.
If you are setting this pistol for general hunting and shooting, then you would likely go a different route.
Originally Posted by TexasHunter
I think my first build will be a 30BR with 12" 8 twist tube. I will be able to have almost 308 level performance on one end and load heavy bullets with trail boss for whisper performance with my 308 can.
For the second barrel, I'm thinking 16.5" in either 6.5-284 or straight 284.
Any thoughts from you guys?