Hey congrats on buying a OOW semi BAR, I love mine.
I had that same exact same problem with Magazines that I bought on line at Gun Brokers, I bought 14 magazines and only four worked, 10 would not lock into the rifle. I used my Micrometer that I reload with, and started measuring the Good (New) mags that worked and came with the Rifle). I found that the back top of the Mags should be no wider than 1.10" max. If they are too wide, I discovered that they would drag and pinch into the receiver, and won’t lock up with the mag catch. The new mags were .98"/1.0"wide at the top rear. After I discovered that fact, I used a large pair of Channel Lock pliers’ and squeezed the top rear Slowly into the Size that would fit into the rifle, (.98” to 1.0”). When I did this, I found that the lips of the mags would bend in just a little bit. So watch for that issue. I then took all the mags back out to the Range and test fired each with 5 rounds each, if that worked I filled them with 18 rounds, and fired as fast as I could. I still had two mags that were still bad; at that point, I threw them away.
I hope this helps. (BTW...........ALL OOW BARS Come with 2 NEW Mags.) Larry