In general the CETMEs, since the receiver is essentially a G3 reciever, will take G3 mags. Or should. My CETME Sporter would not take some of my alloy mags from CTD(though it would take the curved CETME mags and some of the more worn HK mags) until I sanded certain contact points down and they still fit durn tight. Some so tight that I can't push the mag release with my finger, have to use my thumb. Normally this means the mag-well is out of spec, the mag catch hole was made incorrectly(Too high, too low etc) or the mag catch was installed incorrectly. Depending the situation, a little dremeling on the mag catch can solve the problem.
No experiance with the steel HK mags but the steel CETME mags are heavier than the aluminum mags, without much add strength IMO.
