I just tried a few magazines on my 1992 Sporter barreled receiver (no trigger group installed) and noticed some of the cheaper Korean magazines (purchased from Primary Arms) don't line up flush, some of my older used mags (manufacture unknown) seated nice and flush, Magpul magazine seated fine also, had a 5 round magazine that is wobbly though, so you might want to try other manufactures also, and then I tried the same random magazines in another 1993 Sporter with LuckyShotWoodStock and had to fight to get the Koreans in (and out), Magpul and the unknown magazines no problem.