Be sure you're loading 5.56NATO or .223 and used in the correct barrel.
THEY ARE NOT THE SAME. Just like 7.62NATO and .308 Winchester are not the same.
Here we go again...........
The Brass is interchangable. CAN( notice I didn't say IS) the brass be SLIGHTLY different? Yes, ANYTHING that is a different stamp, lot, day, CAN be different.
The Dies are the same, regardless of capacity(not case weight, CAPACITY) outside dimentions are the same. The INDIVIDUAL round pressures are allowed to be higher on the 5.56 Vs 223. But the average is the same, Reference any of the TM's floating around. The specific readings are done differently, and the numbers CANNOT be the same because of it. Moreover SAAMI warns against NATO in SAAMI chambers, BUT DOES NOT warn against CIP 223....Which IS THE SAME AS NATO; anyone else notice the issue there?
The 5.56 Vs 223 HAS a longer throat(leade) spec than the 223; NOW, but started as the same. Standard QC passed ball ammo in a SAAMI spec barrel will not have an issue jamming the lands. VERY long OAL ammo in a VERY short SAAMI barrel CAN(not does) have a problem.
The 7.62 Vs 308 has ONLY EVER had one spec. Dies are the same, "spec" pressure is the same, brass is the same. Again CAN there be a capacity difference? Again read above.
IF you have a MAX load, or an inconsistent OAL, or a powder that doesn't respond well to temp changes; AND you change brass, or ANY OTHER COMPONENT, YES you can have an issue. Don't confuse changing components without work-up with: The brass is different, and can't be used!
Because of this very issue I talked with Nosler, Hornady, and after a lot of chasing, Remington.
ONLY Hornady admitted to "shooting for .001" thicker case walls on the 5.56. The rest told me it was all the same, excepting the headstamp. All agreed that the brass material was the same, as was the annealing process between headstamps. The above posted capacity chart, is the third different that I have now seen; all agreeing that any differences are standard lot variations.
Remember this definition:
"Interchangeable - capable of replacing or changing places with something else; permitting mutual substitution without loss of function or suitability; "interchangeable electric outlets" "interchangeable parts"
Are they the same? Possibly not. Are they interchangeable? Yes.
Any decent reloader knows when something is substituted, to test it FIRST. That way ANY minor difference is totally irrelevant.