Lets take a look at this chamber info, BTW the external dimensions of the case is the same, but the leade in the chamber is not.
Here is a good article on the 223 & 5.56x45 & 223AI, the differences, etc.
223 Rem + 223 AI Cartridge Guide
For those who won't take the time to read the complete article, here are relevant statements on the 223 vs 5.56
" While the external cartridge dimensions are essentially the same, the 223 Remington is built to SAAMI specs., rated to 50,000 CUP max pressure and normally have a shorter throat. The 5.56x45 is built to NATO specs, rated to 60,000 CUP max pressure and has a longer throat, optimized to shoot long bullets.
THAT said, there are various 223 Match Chambers, including the Wylde chamber, that feature longer throats.
And they said "Should YOU be worried about shooting 5.56x45 ammo in a 223 Remington, THE ANSWER REALLY DEPENDS ON YOUR CHAMBER.
Well, now, hmmm! Of course one has to measure the chamber & plenty of gauges are available & now the design capabilities of your rifle even if it has a long throat.
But it is not a special figure 8 chamber with switchbacks and U turns.
Anyway, I have the 223 chamber, the Wylde & the 5.56 in different rifles. Somebody said something about advise, well No way would I shoot 5.56 in my Contender barrel for example, it has a short throat & not overly strong. And don't assume your chamber to be the exact same as another identical model and spec rifle , sometimes they aren't.
But in the Ruger Am. Predators I have heard about so far, the throat has been ample & the rifle is build very strong, esp. if compared with a MIni and such. But measure yours when you get it.
As far as steel cased stuff, I don't know why bolt guns are singled out for not using that stuff, I have a RRA Varmiter (Wylde Ch) that I would not shoot that stuff in.
Anyway, to the OP, just do your research & I look forward to shooting 75 A-Max in mine when it arrives.