Welcome!

You will find the information you seek by doing a search; this topic has been discussed here at length many times.

Savage does not recommend using 5.56 ammunition in their 223 rifles, but *newer* Savage 223s have loooooooooooong throats whereas older rifles, such as yours, likely have SAAMI 0.025" freebore throats. I know my very early staggerfeed 12FV 223 had a SAAMI throat, whereas a newer Hog Hunter was at least 0.10" (yeah, that much) longer.

It is safe to say that many shooters run handloads in their 223 rifles that are higher pressure than 5.56 loads.