The best replacement for 308 is 270.

The best alternatives to 308 are rated as following:
★★★★★  270
★★★★  223
★★★★  7.62
★★★  30-06
★★★  300 win mag
★★★  243
★★★  7mm
★★  338
★★  300
★★  30 06
★  30-30
★  556
★  7mm-08
★  7.62x39
★  7.62 nato
★  7mm mag
★  3006
★  6.8
★  300 wsm
★  300 blackout
★  7.62x51
★  30
★  223 ar
  7.62 x51
  338 lapua
  30-06 ballistics
  260
  7mm 08
  30 30
  6.5 creedmoor
  270 rifle
  7.62x54r
  270 winchester
  30 06 recoil
  6.5 grendel
  50 beowulf
  35 whelen
  30-06 recoil
  270 recoil
  6.5
  7mm08
  7.62 x39
  5.56
  8mm
  7.62 x 39
  25-06
  7mm magnum
  280
  ak 47
  30 06 caliber
  30 06 ballistics
  25 06
  328
  7.62 ammo

Your alternative for 308 is not listed? Suggest!
Speaking about 308, one probably shouldn't forget about 1 in 10 twist.

Other search terms related to 308 and their ratings are:
★★★★★ 1 in 10 twist
★ 1 in 12 twist
You have in mind a companion for 308 and it is not yet here? Propose!



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308
270
223