Well, I tried my fake "W" marked magazines I had bought and they held a full 20 rds, worked okay manually feeding them through the rifle. But the main issue was putting them in and getting them out of the rifle!! I've NEVER seen or felt magazines that tight in any rifle that I've owned that used detachable magazines. Hopefully they will wear some, since I haven't actually fired them in the rifle yet. Although I have an original BRW S-I magazine and it fits tight also, but not as to the tightness of the others in getting them out. I took the BRW S-I apart and it is an original body, but not the follower from the pictures in the PDF on identifying the fakes and originals. Just hope this information might prove useful to someone in the future if they have bought the "W" marked ones like I did before finding out the differences. I will be buying the Checkmate Industries magazines in the future for my rifle.
Many thanks to you Lee for the very valuable information.
I don't drink, but have a beer on me Lee.