Not sure if twin rifling is any rare or anything, but it seemed odd when I first heard about it.

Idk if it would apply to all rifles in every part of the barrel, but there is a thing called "buzzing" which is where something metallic and somewhat loose is in contact with the barrel when it fires; the vibrations down the barrel cause the 'buzz' on the other metallic thing, and as far as I know this can mess with the harmonics of a standard issue enfield what with its up pressures to tune the harmonics. It may or may not apply to the sight protector, but I would wait for someone more experienced to have a say.

If there is nothing else wrong with it you might as well go take some shots and see if it is alright or all over the place. If it shoots wild then you start fiddling.