I've got some of them and they feed just as well as my p-mags and Troy battle mags. They are not pretty or as well made as the other two but they feed just fine in my rock river. No modification required.
"No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government"
-- Thomas Jefferson, 1 Thomas Jefferson Papers, 334