Ditto on the mags. The best mags are the aluminum USGI or English SA-80 mags. Also you might want to put in a stronger extractor spring (available from Wollfsprings). If it is a M4 length barrel the gas pressure during extraction is very high due to the gas port being closer to the chamber. The bolt will often rotate so fast that the extractor will swing outward due to centrifugal force and not grip the cartridge. A stronger spring and maybe a pigtail gas tube are in order if it is M4 length. If it is the 20" barrel I would remove and clean the extractor and put the M4 spring in (couldn't hurt
) Also check the chamber for reaming marks or burrs that might impair extraction.