I asked if you could shoot 5.56 NATO in their rifle. Browning said NO. CZ said YES.
Simply a CYA thing for Browning in the very rare event smething bad. There are very minor differences between some 5.56 rounds and some 223 rounds. Same with some 223 rifles and 5.56 rifles.
What most people don't realise is that you will see just as much variances between different brass, ammo and rifle chambers in any other chambering. Often a Remington 270 chamber will vary slightly from a Winchester chamber. You will find that at times Federal 270 ammo is loaded to very differnt pressures than Hornady 270 ammo and with slightly different brass specs.
But since we have 2 names for the same cartridges in 223/5.56 as well as 308/7.62X51 it causes confusion. You may well run into a rare 223 rfle that will give issues with some 5.56 ammo. But you are just as likely to run into a 270 rifle that has the same problems with some 270 ammo and not other 270 ammo.