Another mass shooting.....

[The Grand Nudger]

You understand that, before guns arrive at the "used market" they must be new, right?
It seems far from possible to enforce any kind of control on the used goods market, so the best bet would be a generational struggle to close the tap upstream.

Not in the US.  We have so many guns that production of new guns i already..largely, an export market.  They made a mint of the AR15 of late, due to the brilliance of the three gun marketing campaign.   Remember that most of these guns will -never- be used in a crime, areas with the most guns statistically see lower rates of gun crime -and- gun death, and guns hold their value at floor for decades.  There's no reason to suspect, in this situation, that making more guns or fewer guns will qualitatively increase or decrease crime.   There are already enough guns in circulation to perpetuate gun crime indefinitely.   

Well... yes they will become less lethal, as they age, rust and break.

I agree with you that such practices should also be employed. Also.

They're durable as shit.........most of my guns are older than me....one of them was made before the civil war.....

Your efforts are going for the largely uncontrollable P2P second hand market.

A market that needs to be closed.  There should always be a licensed dealer and a background check involved.  

They could be controllable if the guns currently in circulation had been purchased with a proper registration and require that registration to be updated at a central location every time the gun is sold, like you'd do with a car (at least that's how we do it with cars where I come from).

That'd be newer guns......factories stamp them and even file the rifling pattern nowadays.  This is in addition to other features both employed and in the works that make them safer.  Consider this, if we bought the old pistols off the streets....the pistols remaining in circulation could be much better regulated.  Hell, we could mandate that they all be sold with fingerprint locks.  There's a requirement for manufacturers they;d be all to happy to comply with.  Costs more.

Any crime committed with that gun would ultimately be traced back to it's registered owner, and no one wants to be guilty of a crime committed by their old guns, do they?
Start now! Implement this, if it's not already in place. Confiscate and destroy any unregistered weapon.

Americans have an aversion to government agents confiscating their things.  You're familiar with our government, right?  It's not an entirely unwarranted fear, lol.

While, at the same time, constraining the ease of access to new guns.

Gun confiscations aren't a reality in a pre gun-ban US.  Thems the breaks.  State level registritation and registration requirements are already a thing. Buybacks and pos control are much more feasible, and produce the same effect.  Trouble is..we couldn't afford to buy them all...so I say we start with the ones we keep confiscating from criminals..the ones we keep finding at crime scenes.  9mm's manufactured before '06. Then we can move on to the next category. Revolvers.......,
then the next....rifles, -amusingly, the only category in which "possession" is the major initiating offense, iow..felons who buy deer rifles.
then the next, shotguns,
then the next, "unknown types"
then the next, derringers (tiny pistols)
then the next, machine guns and assault rifles.

Notice...above, that homemade guns (unknown types) are better represented in trace data than the assualt rifles......I;m not saying we shouldn't do anything about assault rifles (the real ones and the ones that people think are assualt rifles)...I just find it amusing that a Home Depot Special get's higher placement in the trace.