Sorry to awaken a slightly zombie thread, but I didn't want to create a new review. I picked up a couple coupler magazines. They seem pretty well made. I haven't tried them in a lower or shooting yet, but I did drop them on my hardwood floor. The coupler comes apart pretty easily, I'd say about 50% of the time. I was dropping from shooting height ~4-5 feet.

I visited the ETS booth at SHOT Show today and asked them about this issue. They said that there are two possibilities:

(1) The mag ridge that I showed in the picture is hitting the lower receiver and preventing it from going into place. (This is what I thought was happening, as explained earlier.) That ridge is there deliberately to prevent over-insertion of the mag, so if you have an oddball lower then there could be a problem. They suggested using a Dremel to cut back the ridge on the mag if there's an issue.

(2) The rep said that some bolt carrier's aren't cut properly and have too much material on the bottom, and the feed lips on the mag can interfere with the bolt carrier. ETS will be coming out with a "version 2.0" at some point that has less material at the top to prevent this.

The way to test which issue you have is to remove the upper and just insert the mag into the lower. If it goes in fine, then the problem is with the bolt carrier. If you still have the problem, then the issue is with the ridge on the mag hitting the lower.

I'll have to go play with mine some more . . . .

Uh hunting, and 1000 rounds don't typically go together in the same sentence. What were you "hunting"?

Either an accurate zero or prairie dogs. Pick whichever one you like best.

Haha ... yes, prairie dogs.