They are already on the black market. Hell people in prison still find ways to make crossbows and kill each other. With the insane amount of undocumented guns (like every gun I own) on the market, it would be impossible to find and stop the sale of firearms.
All you accomplish is turning a large majority of americans into criminals while preventing law abiding citizens from defending themselves. Existing people already using firearms illegally will have no effect to their day to day operations (With the exception of their job getting easier).
Firearm bans worked well in places where there were registries of all owned firearms. Do you really think the majority of americans would tell the government how many guns they own? I'd argue the popularity of firearms would increase if they were banned. Look at how sales spiked on assault weapons just because of a rumor (without proof) that obama's election would cause a renew of the assault weapons ban. Look at how hard it is to find high cap mags right now after the recent shootings.
I'd argue that the guns are a point of pleasure just as much as booze. I own many many guns, most for pleasure. I own many many bottles of rare and strange booze, again mostly for pleasure. I rarely use both (and never use both at the same time).
Raising education would solve a lot of our problems a lot faster then banning anything that can be abused. If someone wants you dead, they are going to find a way to attempt their goal. Car, gun, spork, poison, or even their own bare hands. Murder rates are now lower just because guns are banned, murders from firearms are lower because guns are banned. If a guy comes home and his wife is banging his best friend, he doesn't go "well, I don't own a gun, so let's talk about this". He grabs a knife, or vase, or golf club and beats him to death. If he was going to talk it out he would talk it out with or without a gun.
I've owned guns from the time I was old enough to point one down range. I even owned scary black guns and wore a trench coat in high school. Being educated in the PROPER of firearms and in morals, ethics has made that gun ownership responsible.
To put it another way, you have more to fear from my cooking then you do my M1.