Anyone who has been paying attention bought their ammo long ago.
That doesn't mean that newer people to the shooting sports have adequate supplies, and competition shooters (at any level) go through a lot of rounds.
Maintaining proficiency with a handgun, and to some degree, even a rifle, requires practice.
This sort of legislation will only open up a black market in ammo, which will ultimately mean more profit for criminals, not less. Even the making of the possession of small quantities of certain drugs a Felony has not deterred a vibrant trade in those substances.
The regressive nature of making ammo more expensive and difficult for the law-abiding to obtain falls most heavily on those of limited resources, often the elderly and poor who can't afford gated communities and private security, and whose defensive options against the criminal elements in our society are limited to self-defense.
Keep in mind that the millions of invaders who have been let into this country by this administration are likely to coalesce into communities where they will not assimilate, but form ghettos, displacing those of lesser means, even though they, themselves are unlikely to be living in the high rent districts. For the citizens who already live in those areas, the probability of becoming victims of crime or violence will increase at a proportion greater than for those in more upscale environs. Again, for all practical purposes, the defense of self and household for those citizens of lesser means will fall upon the individual citizen, as existing law enforcement, even where it has prosecutorial backing, will be sorely taxed to keep up with the changes in demographics. If New York City is overwhelmed, with all its resources, Small Town America will feel the crunch even harder.
Predictably, crime will rise. Recall that mass shootings require, by definition, four victims to be considered such, and a single box of ammo will suffice for those who are of ill intent. It does not matter how many cartridges they have in their car trunk, what matters is how they intend to use them and how they are employed. With the increase in mobs engaging in crime sprees, diminishing the ability of homeowners or tenants to legally defend against large numbers of criminals at once (by reducing available magazine capacity or the availability of semi-automatic firearms) only leaves those people less able to defend themselves, their families, and their businesses.
The problem is not one of having access to ammo.
There are already laws in place which prohibit most of these people from owning a firearm. What does matter is the number of people who have exhibited homicidal tendencies on top of existing records of violent criminal behaviour, who consistently seem to slip through the cracks in the mental health system and in the NICS system. Perhaps that would happen less if so many mental health resources were not being devoted into convincing children that their plumbing needed to be surgically restructured to make them into a parody of something they were not, and instead were devoted to dealing with those who exhibit violent criminal behaviour.
Obviously, incarceration of those who have committed violent crimes is one approach that seemed to be relatively effective in the past, as well as the use of the death penalty for those who had committed the crime of murder. The same reforms which have appeared to leave the cracks through which most mass shooting shooters have fallen have also removed much of the prosecution of violent and property crimes.
If we do not enforce our laws, more laws will only provide the means to attack people who were not a problem, while the truly malicious criminal elements are free to roam and commit mayhem. Enforcement and prosecution of offenses committed with current laws would work, but only if such is carried out without any preferential treatment based on race, creed, or color, or whatever other reason for being treated as if the perpetrator could do no wrong. Lenient sentencing should be reserved for the rare and unusual cases where it is warranted, not be common practice,and the use of high bail amounts to secure those who have been charged with violent crimes could prohibit them from committing other crimes while out on bail.
