hi everyone ive been searching my question & cant find an answer so here i am. i just bought a rock river ar-15 5.56 & the magazine it came with is a 30 round thermold magazine (its plastic in case you need that info) i can pull the charging handle back, release & it only goes forward about a half inch mayby less. the round wont come out of the mag & feed into the chamber. if i put pressure on the bottom of the magazine while i pull back the charging handle & release then it feeds fine. magazine is slightly loose in the well, idk how tight or loose an ar magazine should be in the well. all ive done is test its cycling hasnt had a round through it yet. i just hope someone knows what would cause this. thanks for any info