The cut-off could only be removed in an Armourers shop. Not possible for an average sniper to do so. And if an Armourer removed it, same as on a No1, they were aware that it would just be another hole/slot for dirt. dust and other crap to enter the rifle. Designers also knew the phrase that 'dust and dirt are the arch enemy of magazines'. That's why they welded the view holes up on sten gun magazines.