I didn't want to make a new thread on the same thing, so I'll ask here.
I just received one of these for the M16 series in the mail today, and I'm still trying to get it to feed 100%. For one, what does that button-twisty thing do on the right? According to the directions, after loading you should push the front side of it so the back pops out, twist it until it stops, and then pop it back in...? It seems like that resets it to me. I really have no idea how it's helping at all... I misfeed about 20% of the time, however if I push up on the bottom of the c-mag I encounter no feeding problems even for a 15-20 second burst...
BTW, I also recommend this C-Mag! It's great for the price and it feels solid as all hell. I haven't had a problem with the batteries falling out like Jackals, however. I accidently dropped it off a ~1.75 meter shelf with no problems.