I recently purchased 5 of your Lancer 20rd, i think its the new version as there arent any thick ribs like my first gen 30rd.
Last week at the range I would fire 3-4 shots and then CLICK, the bolt didnt pick up a round. I was only having this problem with my Lancer 20rd mags. There was a clear scratch from the bolt all along the next round in the magazine.
Im thinking it may be a spring issue?
Send me an email and we'll look into it - firstname.lastname@example.org