The best replacement for .223 is 5.56.

The best alternatives to .223 are rated as following:
★★★★★  5.56
★★★★  .308
★★★★  .22
★★★  .243
★★  7.62
★★  5.56 ammo
★  22-250
★  7.62x39
★  .22-250
★  9mm
★  30-06
★  300 blackout
★  5.56 nato
★  .270
★  .204
★  5.56 ballistics
★  5.56 bulk ammo
  30-30
  22 250
  .224
  .22lr
  5.62
  6.8
  5.56 difference
  .22 250
  .17 hmr
  30 06
  .243 ballistics
  .243 rifle
  .45
  5.56 cheaper
  .222
  5.56 which is better
  .22 lr
  nato
  bear
  6.8mm
  .223 rem
  6.8 spc
  .22 caliber
  5.56 ammunition
  7.62 x 39
  .204 ruger

Your alternative for .223 is not listed? Suggest!
Speaking about .223, one probably shouldn't forget about 1 in 9 twist.

Other search terms related to .223 and their ratings are:
★★★★★ 1 in 9 twist
You have in mind a companion for .223 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of .223 in all years. Click on graph for more.
.223
5.56
.308