I used a small screwdriver to bend down the front of the bottom plate of the mag enough to clear the tab. With the small screwdriver in place, a pin punch in one of the holes of the bottom plate can be tapped lightly with a small hammer to drive the plate forward.
Re-assembly is accomplished by using the same pin punch and small hammer to push the plate back into place.
You can de-burr the feed lips, round the tabs and chamfer the front of the mag without dis-assembly by using a wood dowel to depress the follower enough to allow a stone or fine file to access the lower edges of the feed lips etc.
Trigger control + Breath control + Sight alignment = Gun Control.
NRA Smallbore Prone Master, High Power Master