When I was shopping for stripper clips I did all the reading, all the research, and, still, I didn't pay attention. I got the crappy NcStar ones and spent a ridiculous amount of time tweaking them just so they would kind of work. They never worked well at all. Either the rounds would fall off with the slightest jiggle, or they would fight against being loaded into the carrier. Garbage.
Just get the stripper clips marked BXN or BXN 65, or any other variation. You can get them on Ebay for $0.50 to $1.00 a piece, shipped, depending on quantity and who's selling at the time. I have genuine Chinese surplus and Yugo surplus clips, and those are good -- a million times better than the new knock off crap -- but the BXN's are even better.
Save yourself time, effort, and in the long run, money, and get some BXN's. They work beautifully. I wish I'd paid attention in the first place.