So...what do we think about .458 SOCOM mags or .50 Beowulf mags? I don't see how they could be illegal, as they only hold 10 rounds of that certain ammo...Hell you can't even fit more than 8 or so 6.8 SPC rounds into one of them either...

Even if you don't have the upper yet, it's not illegal to own a magazine for a gun you don't own...right?

And even if they are marked for 5.56, that doesn't mean anything since they are identical.

And hell...a ten round .40 cal Glock mag can hold 13 or so rounds of 9mm...does that mean all ten round .40 cal Glock mags are now illegal in NY?

When you are standing before a cop (who is somehow still on our side), and you tell him that this 30 round mag isn't a 30 round mag, and he can't have his felony arrest, because it's actually a .458 or .50 mag, you will see his eyes light up, because by trying to talk your way out of it, you admitted that you knew that 30 round 5.56 mags are illegal, which means he doesn't have to give you the 30 day warning period (assuming he ever would, because it's easier just to arrest you and let someone else worry about it--that's how bureaucracy works). Then this cop (who is somehow still on our side and not a collaborator at all) will put you in cuffs and take you down to the station, and you can explain to a jury of people who know everything about guns because they watch Law & Order, that this evil 30 round mag is not actually a 30 round mag, even though the prosecutor just showed them that it can hold 30 rounds, because it can also hold 8 rounds of this bigger fatter bullet, and somehow that makes it okay. They will deliberate for about 30 seconds before finding you guilty.

Other than that, should be good to go.

My 50 Beowulf mags weren't identical to 5.56 mags.

I made minor changes to the feed lips to get the top round's nose to sit up higher and feed better. Making them prone to double feeding if you tried putting anything else in them.

So if I own .40 cal glock mags, but no .40 cal glock, then I am in possession of a high capacity 9mm magazine? Because .40 cal glock mags hold more than 10 rounds of 9mm, and function perfectly.

So if I own a 10 round .458 socom mag (which is the same as a 8-9 round 6.8spc mag), then I am breaking the law?

Again I don't have any, just trying to think of some legal defenses for people who may get arrested wrongly for having a standard mag.