Extractor not extracting

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So my Pederson block developed a crack across the breech face. I ordered a new block from Century Arms Surplus Store.  I installed the old firing pin and the old extractor into the new block.  The only problem now is that it doesn't extract the fired round about 1 out of every 8 to 10 shots.  The extractor seems to fit in the rim properly and is in the proper position relative to the breech face. The R51s have a roughly finished chamber which scrapes up the brass, but the spent case is not expanded enough to get stuck.  The spent case will fall out the chamber easily.
Any ideas or fixes that worked on your R51?