Pretty hard to diagnose not see seeing all the parts but I think Blue is going the right direction with the extractor being the problem.
Never used a Sharpe BCG so no idea about their issues or not.
Take the bolt out of the carrier, remove the ejector & see if a case rim will easily slip under the extractor & if it appears to have enough surface gripped. Are there any extractor marks on the fired brass?
About all I can say at this point other than try another bolt or another extractor if you have on available.
MM
