Yeah, you're going about it ass-backwards. First, you want to meddle with cheap things before expensive things, so don't screw with the rifle when you can easily modify magazines. Second, as stated above, magazines vary, especially the non-metal ones. It is common to have to fit various magazines to your AK. You might want to take a couple of file swipes on the ramp of the rear lug of the mag and see how much you have to take off to make it work. Mags also sometimes need to be relieved on the upper rear corners if they are jamming on the mag guide pin just inside the rear of the mag well. Don't mess with the pin, work on the mag which is easy to replace if you screw it up. About the only other thing that happens is sometimes the sides of the polymer mags will scrape. If you get gouges on the sides, look inside to see if the mag guide rails need to be filed flat.
I had to fix a steel mag at the range today because it didn't want to lock. I saw that it was jamming on the guide pin so I took the mag and drew it along the side of the concrete shooting bench on the upper rear corners a couple of times and it was enough to make all the difference. I did finish the job with a file when I got home but that trick saved me a lot of aggravation at the range.
Anytime you're doing something like this always do things in small steps - you just want to get it working, and too much will make it sloppy. You can always do a little more if it still doesn't work.