I just got the Beryl AK rifle in 5.56 and both the ac unity ak19 and standard 5.56 mags to try out. I was surprised how well the RB Radom mag that came with the rifle fit. I've never had an AK mag fit so well it was perfect and clicked right in with no slop or wiggle. Now the ACU mags were a different story i had to shave down the plastic above and below the rear lug . Above the rear lug allowed the mag to clear the safety stop plate. (one could just keep inserting the mag a hundred times to shave off the plastic ) . Below the lug allowed the mag catch lip to seat all the way against the magazine body. I also filed down the bottom side of the rear lug like so many people have suggested and this allowed the mag catch latch to completely seat. Fitment was solid and i was able to get a similar click in fit like the FB mag.
NOTE- You can file and file on the bottom of the rear lug and not notice the plastic above the rear lug is snagging on the safety stop plate.
Extra small parts below that came with the rifle. I had the additional left side selector and pin on brake added.
The way i fit the ACU 5.56 mag to my Beryl. Pictured below is my Work Sharp knife sharpener that helped sand the area's pictured.
1. I lightly sanded this are to allow the mag to clear the center support rivet/post. Dont go too much or you get back to front looseness.
2. I filed/sanded the bottom of the lug to allow the mag catch to close fully.
3. I filed/relieved this area to allow the mag catch to clear the plastic and fully close. NOTE : I also relieved the area above the lug to clear the safety stop plate.