It worked with another carrier and bolt, but not with the OEM? Hmmm. If it didn't work with either I'd check the buffer/recoil spring, but since it works with one and not the other, I don't know. Are there marks from burrs on the inside of the upper, or burrs on the carrier that might be causing it to drag? That's all I can think of, since it works with another carrier/bolt.

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