SAAMI's for the .223 is 55,000 psi while MIL SPECS for the 5.56 is 62,400.
See US Army TM 43-0001-27, chapter 10:
i can find one case where rifles blew up using .223/5.56mm ammunition. Those guns were destroyed while firing Winchester Power Point .223 ammunition:
On 02/14/11 an officer was attending an M4/MP-5 class and during a shooting session, the .223 rifle (Stag Arms) experienced a catastrophic failure resulting in an upper receiver cracking and the bolt being pushed into the bolt assembley.
During a SWAT training day on 02/23/11, three more M4 style rifles experienced a catastrophic failure at the same time. All three rifles experienced the bolts being pushed into the bolt assembly, the upper receivers were cracked and / or broken apart, and the lower receivers were bowed outward. The ammunition we used in all the rifles were Winchester RA223R2 Ranger 64 gr. Power Point.
The Rifles were: 1-Colt, 2- Bushmasters and 1 – Stag Arms