At this point I might take it shooting with the HG removed to do some testing. IIRC this is an SASS barrel and GB right? This eliminates the abilty to use an adjustable block without making one yourself. Maybe try either an adjustable or pigtail gas tube. If this is not an SASS you might be able to machine the hard corner off the boss ans eliminate the high spot. If you try the adjustable tube or gb go to the range with the HG off. In the end if reducing the flow solves the problem you can probably mofify your gas block with a smaller hole permanently. Also JMoto there is absolutely nothing to lose polishing the chamber. Even if it is ok it will be "more better" :) for your effort.