Sounds like the gas tube or gas block isn't sealed quite well enough, creating lower gas pressures. Or, it could be that the gas port is plugged with 10+ years of gunk from the safe, thus creating the lower pressure.
Before you go tearing it all apart, I would suggest checking putting it on another lower that works, so you can rule out the buffer/spring combo. Once you eliminate this, then you can check on the gas system.
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