We could get into another argument over exactly what kind of "arms" are protected by the 2nd Amendment here. Hopefully we can limit this discussion to "portable firearms" and not crew-served weaponry or artillery/RPG type weapons.
From my reading, Scalia is saying that to ban rifles like the M-16 would require detaching the right from the prefatory clause (A well regulated militia being necessary to the secuirty of a free state, ... and that this cannot be done for reasons articulated in the decision.
I think this leaves open the question of whether or not closure of the NFA registry and the ban on transferring new Class III firearms are permissible.
In the second paragraph, Scalia addresses the argument that pitting small arms against modern armor and aircraft makes the whole militia-vs-tyranny argument silly. But he says that while technology may create such an argument, it cannot change the validity of the right (as the court interprets it).
Further court decisions will be required to make sense out of which firearms are "in common use". Certainly, the AR-10/15 series, AK/SKS series, HK-G series semi-auto rifles are in common use, as are the Barrett .50 rifles. But are M1928 Thompsons? Uzi and Ingram SMGs? How about .30 and .50 caliber Browning MGs?
I would suggest these are "in common use" but also limited use due to current restrictions and the cost of the firearms and ammo. One could argue either way with the M-14 rifle since few were ever sold as surplus. But there is no doubt they would be in common use if they were made available as surplus rifles like the M1 Garand.
BillCA in CA (Unfortunately)