Using USGI 20 rd. mags, the last round continually does not feed.  The bolt rides overtop of the round, and doesn't strip it from the mag.  This happens with several mags, not just one.

I opened up the feed lips slightly to allow the round to sit higher so the bolt can hit the case rim better, but this didn't help.  I can't raise the lips anymore, or else the bolt doesn't travel back and forth properly.

I already have green followers, and Wolff extra-power mag springs.

Help!?

Does it lock open on an empty mag? Will it lock open when the last round is fired out of a mag?

[edited for speeling]

Yep, locks open on an empty mag - as it should.

If it's not short stroking then perhaps the mag catch is located wrong. Send it back.