I believe so and here's why. The 7.62x39 is a tapered cartridge and therefore requires much less force to extract vs. a "tube" style cartridge that inherently has more friction such as the 5.56 design. Thus, a smaller extractor on an AR style bolt makes sense to me. Or a fluted chamber like the Germans did with the G3.if the extractor was made a bit thinner--giving a little more meat for the lugs to hold to the bolt? would the extractor still be functional???
I don't know how small it could go, but couldn't you also have an extractor that straddles a lug, providing 2 exractor fingers touching the base? Just thinking aloud.