Bartlein barrels I'd trade for:
.243 #3 or Remington Varmint/ Sendero 8 twist or faster
.264 #3 or Remington Varmint/Sendero 8 twist or faster
.308 #3 or Remington Varmint/Sendero 10 twist or faster
.224 #3 or Remington Varmint/Sendero 8 twist or faster