Well, to be completely fair, and as unbiased as possible, I'd put forward the following argument:
It wasn't an issue so much of the notion of private citizens owning guns and other forms of weaponry, military or otherwise. I don't think the British were making the claim that private citizens could not legally possess guns. Rather, the issue was more about who owned the guns/weaponry: the Crown or the people of Massachusetts by way of their provincial government. The Crown would argue that the weaponry to be confiscated---cannon and powder---were the property of the "legitimate" General Court, which was nominally British and loyal to the King. The radicals would argue that the old rules no longer applied: the MA government was no longer represented by the old guard but by the provincial government, and therefore, they owned the munitions.
All of this, of course, doesn't really matter, because possession is nine tenths of the law.
So while yeah, Lexington and Concord was a gun grab, it wasn't a "gun grab" in the way we use the concept today.
I would expect to hear that argument but I don't believe it is correct. I can't lay my hands on the references now (my books are all boxed up) but I believe the cannon were privately owned. The powder was probably a mix of private and gov't. The powderhouses worked a bit like a bank. You could store your powder there retaining a chit to retrieve it as desired. It was safer that way as the old black powder was a bit unstable.
You can bet there was a surge in private stockpiling of ammo then just as there is now.
You’re right, the crown wasn’t concerned with the ownership of guns per se, they acted because the townships in the colonies, especially those in new england, had begun forming and drilling militias for the first time since the French Indians wars. With the rising tensions between them and the mother country it wasn’t hard to figure out why.