

I've found Magpul E-mags work best of polymer magazines in the magwell adaptor but you still need to do some minor alterations to them. You needs to cut/file the back of the mag like below it order for them to insert properly;

And you may need to file the top of cut in the side of the magazine that the mag latch fits in to make it deeper and allow the mags to catch more easily. I'm sure I did a thread on this somewhere but good luck finding it!
N.B. GI steel and aluminium mags work without any modification