What new chamber on a 6mm 14 t?

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I have a Panda 6mm ppc that shoots as good as I can. I have 3 extra barrels in 6ppc, [14 twist] that were bore checked and I was told they are fine. I am thinking of a rechamber on one. It will be a 100 to 400 yd gun. My bolt is 6ppc / 308. What are your thoughts?
thanks Don

 

[TAJ45]

What else, BR, orrrr XC to really launch the rodents.

 

[Dusty Stevens]

6 ppc

 

[Dusty Stevens]

6 grendel

 

[Shawnba67]

6mmAckley! that extra 700fps cant hurt!

 

[swd]

6BRA and see what the darling of mid/LR will do closer in.