With the SA/Denel 7.62 BBLs you need to use the SA-specific 7.62 extractor.....i am running the same combination of parts as you in my all-original '42 Daimler MG and when using a .303 bolt + SA 7.62 BBL you need the SA extractor for reliable extraction. Inglis 8mm and L4 7.62 extractors don't work reliably with that combination. You can get SA extractors from Dave Selveggio@ DSArms. Probably have to ask specifically as they aren't on the webpage anymore I don't think?
-TomH