I have had the same mag loading issues with my Px mags for the CX4 carbine. I have 17 and 20 round mags and cannot seem to load any of them to full capacity. I don't consider it to be a wimp issue....they just will not go. I can get around 17 in the 20 rounders. I could understand if it was 19 and the 20th was too difficult, but at 17 I feel as if I am going to break something. I can get 15 or so in the 17 rounders. I bought all of these mags new and even re-read the packaging to make sure I got the right ones.