That's why I told you to pay attention to what the rifle is telling you in the other thread. The break in procedures are just to avoid headaches/heartaches of failures at the start.
Your rifle just didn't need parts to wear together. Run it on the lowest gas setting that gets you proper ejection patterns (8+ feet at 2 o'clock). You'll probably also find that the recoil the rifle gives you is pretty soft.
If a large chunk is missing, I'd replace the recoil buffer before shooting again. If it just has some marks, it's probably okay to shoot it until you replace it.