I've only seen a small handful of sks rifles work with the 30 round magazines.
Usually: bang, bang, click, #$%&, bang, bang, bang, &%#&, click, &@#$, bang.....
I've purchased 2 extra 10 round magazines for when I go shooting and someone brings an "sk" (I can't roll my eyes hard enough) or an sks. Alrighty I already know whats gonna happen.
90% of the time they whip out an sks with an extended appendage....
They get pissed that it don't work. I pop in the fixed mag. They are happy until I take my mag back. Then I tell them what they need to find and buy.
I detest to the bottom pits of hell the duckbill 30s.
Physics based reality only permits me to share a small percentage of my loathing for those dammnable devices.