Lol, that was the point of the post...
And my point is that he is looking to a rather grey area. Yes, the magazine should FIT in the original rifle, but it may not FUNCTION in that same rifle it was made to feed. The base plates on every 5.56 and .223 magazine I have ever seen listed the caliber they were made for. The claim can be made that by modifying the magazine to be loaded with a different caliber, he has in fact manufactured a new, post ban magazine.
To alter my Marlin mags, all I had to do was add a notch, but if I had converted them to a different caliber, they would have no longer functioned in the original weapon, thus making them illegal.
He asked about the legality of doing the conversion, I pointed out that it
may have to still function in the old caliber for it to be legal. Just because it starts life as a pre-ban mag doesn't mean it remains one after the modification. I was trying to give a gentle prodding for him to dig up the requirements, and make a choice based on the risk he was willing to accept.
If it's an AR mazine and it's modified to work in an AR, I don't see the problem, myself, especially when it could still be used in a .223 AR, if not particularly reliably. Thing is, it has to work in the original gun, but I do believe that there's no requirement that it can't work in other guns, as well.
This is the point, right here. I can build a 9mm AR, and modify Uzi magazines to work with it, and be legal because they will still work in the Uzi it was designed for. If I modified 9mm Uzi magazines to work in a .45 cal AR build, they would be illegal because they would no longer function in the original weapon, even if they did fit. I did not know if the modification required to make them function in a 6.8 would make them non-functional in a .223 chambered weapon.
The question is, "Will a DA with an ax to grind consider a different caliber of the same type of weapon to be a different weapon?"
My guess is "Yes" because a DA is going to read the law in a way that is favorable to their case, and another charge tacked on is another charge they can deal away, and still get a conviction. Again, this is dancing in the grey areas of the NYS AWB, so tread lightly, and don't blame anyone but yourself if you get in **** for it.