Yeah, I didn't try all my 20-rounders out, but I tried 3, and each of them had the exact same jam on every round in the mag. I figured it was a design thing, but if your 20s are working, maybe it's just me!
It could also be something with my particular rifle. I have read some postings from others on the net and it appears some people have feeding problems with the 20s like me.
I have read that the curved 20s work well pretty universally, though.