Originally Posted by Tommygunarms
On any gun you want to remove as much stuff as possible to keep it from impeding on the gauges, as for the AR you have to remove the ejector and the extractor as for the AK you have to remove the extractor since the ejector is on the receiver.
As for your question about what you could do about fixing the headspace on an AR you can take it to a gunsmith to take off the barrel and have the headspace corrected on a lathe
I have never had that problem myself but that makes sense. I figure you take material off the barrel extension not the upper. I have threaded and chambered bolt actions before under a master Gunsmith. That's why I have probably the only SMLE in 243 win. with that long mag/action a I can shoot them Berger 105gr though my mag not single load