his is something I don't understand about 2nd Amendmenters. He is not taking your right to bear arms, he only wants to keep advanced military hardware out of the hands of citizens

I don't expect to change your point of view, but I'll try to give an honest effort at explaining this for you.

The point of contention is that laws already exist to keep 'advanced military hardware' out of the hands of normal citizens - automatic weapons (Machine guns, assault rifles, SMGs, burst-fire capable weapons, etc.), anti-vehicle weaponry (Rocket launchers, missiles, autocannons), explosives (Mines, grenades, bombs, mortars), vehicle-mounted weaponry (large-caliber guns, cannons, artillery), and other miscellaneous weaponry are functionally illegal - only able to be obtained after extensive paperwork and background checks by federal agencies, and prohibitively expensive besides (i.e. an M16, of the style and capabilities of those used by the US military will easily cost you tens of thousands of dollars - and it won't even be brand new).

These laws have been in place for quite some time - some for the better part of a century, and some for decades.

Background checks already exist - in a capacity that is actually functional and useful. Where the system falls short is that the majority of people who are mentally ill, are not documented as such - either as a result of the red-tape of healthcare privacy laws, as a result of inefficiency and lack of communication between different groups, or, and far more often, simply as a result of these individuals not having been diagnosed or treated for anything more than generic anxiety and/or depression - like a very substantial portion of the population of every Western nation.

The reasons anti-gun control folks get all up in arms (no pun intended) when the subject comes up is that what so many gun control advocates wish to do is ban firearms like the AR-15, mandate 'universal background checks', and limit magazine capacities. There are others, but these are currently and in recent memory, the biggest things being pushed for, and I'm going to address just these three individually.

First, the AR-15. There is a misconception by many that the AR-15 and the M4/M16 rifles used by the US military are functionally identical - capable of automatic fire (or easily modified to allow for such), capable of 'extreme killing power', an unreasonably 'high caliber', and that they are easily obtained and frequently used in the commission of violent crimes. This is not the case. They share many of the same mechanical components and cosmetic features of the M4/M16 rifles, yes. They fire the same round (5.56x45mm NATO or .223 Remington - functionally the same cartridge), yes.

They are not capable of automatic fire, and it is very difficult to modify them to be so - to the point of requiring modern metal machining equipment and even fabricating new parts.

The cartridge, 5.56mm NATO, is not a 'high caliber round', and it is not capable of 'extreme killing power' - it's literally a high-velocity .22 cartridge, and its ability to pierce most police soft body armor is due to it being a rifle cartridge, whereas police body armor is generally rated to protect against common pistol rounds (Given that these are the most commonly encountered firearm threats). Virtually every other common rifle cartridge in popular use in the US is significantly more powerful, and equally or more so capable of piercing body armor. The .223/5.56 is significantly overshadowed in penetration, range, accuracy, and lethality by other, much less maligned rifle cartridges that are just as common - .308 Winchester (Which stands a very good chance at defeating my military combat body armor), .30-06 (Ditto), 7mm Remington (Again, ditto), .300 Winchester Magnum (Again...)

As for easily obtained and used in a large amount of violent crimes...This website debunks just about every myth and talking point that is brought up to argue for the prohibition of 'assault weapons', with links to studies and statistics to support these. Easily obtained? The average AR-15 or 'assault weapon' generally costs in excess of $750, and can easily cost $1500 or more. They are not the sort of firearm that even the average citizen, let alone the average criminal, can afford to purchase and own.

Onto universal background checks. These are often brought up with an argument to 'close the gun show loophole'. First and foremost, the overwhelming majority of firearm purchases at gunshows are from federally licensed firearms dealers (FFLs), i.e. a local gun store that has set up a table to take advantage of the large amount of potential customers. ANY firearm transaction (More on that in a moment) from an FFL to a private citizen requires by federal law, a background check - any transaction. If I purchase a gun online, from a place like Armslist or Gunbroker (Basically Craigslist or Ebay for guns/gun stuff, essentially), it must be shipped from and FFL and to an FFL, and I have to go pick it up from whichever FFL received it. Before I can leave their store with it, they are required by law to conduct a background check just as if I'd purchased it from their inventory.

The only aspect of firearms sales that are not regulated are between licensed dealers (A gun store selling something to another store, or a manufacturer selling something to a store, for instance), which licenses obviously require extensive background checks and time and money and paperwork before being issued; and private transactions - i.e., I want to get rid of a shotgun I have, so I sell it to my neighbor for $200..Just as if I wanted to sell them an old TV.

Now, that second bit, private transactions, that sounds like something that should be required to have background checks, too, right? The issue that pro-2A people have with this often isn't that it's necessarily unreasonable, it's that it's unfeasible and does nothing but punish people who already abide by the law. It's already illegal to sell a gun to a known criminal, a mentally ill person, a fugitive, etc. whether it's me, you, or a gun store selling the gun.

So, enter mandatory background checks - even for private sales. I still want to sell my shotgun to my neighbor for $200...But now I'm required by law to go with him to a gun store with the gun's information, and mine and his personal information, and pay a $15-80 fee to that store to conduct a background check on us both, to ensure we're both legally able to complete the transaction.

Aside from this just being an expensive pain in the ass - what the hell is stopping me from just walking over, knocking on his door, handing him the gun, taking his ten $20 bills, shaking hands, and going back to my house to play Xbox? Absolutely nothing. It's like securing your house with a piece of duct tape on the outside of your door - it provides literally zero functional security. It's worthless. It's a waste of time, money, and legislation - and it'd end up screwing over people far, far, far more than it'd end up preventing crime. Virtually the only people who would be punished for violating this law would be a father buying his son a gun for Christmas, a husband getting his girlfriend a gun for personal protection, a grandpa giving his grandchild his old revolver he got in the 50's, etc. - as these would be private transactions, and requiring a background check per this law, but many people would not realize that they applied to these situations.

And, finally, onto magazine capacities - again, I would like to present this website, about halfway down the page. I don't want to add to my wall of text more than I have to, but it boils down to it being another feel-good law that has no real impact on crime prevention or gun violence reduction, and serves only to inconvenience law-abiding gun owners. It takes 2-3 seconds to change magazines - not nearly enough time to have any significant impact on a shooting where the shooter is expending that much ammunition to begin with (This is demonstrable by comparing mass shootings where the shooter or shooters had <10 round magazines, and >10 round magzines).

I doubt anyone is going to read this in its entirety, but if you have any further questions about any of this, I will try to answer them in a timely manner.

tl,dr: Pro-Second Amendment people aren't against common sense gun laws - it's that common sense gun laws already exist, and we're against useless feel-good laws that just make it more difficult and more expensive for law-abiding citizens to own guns for legitimate and lawful personal use.