This is the .950 JDJ Fat Mac. It is a 100 pound, 5 foot long rifle that shoots a one pound solid brass bullet at 2200 FPS. It is a non-NFA item only because the ATF gave it a sporting exemption as a joke as if anybody is going to hunt with this. This round would be overkill for hunting blue whales.

I would like to paint a picture for you. It's 2AM and you hear a window break in your living room. This is the worst day this could happen, as every single one of your guns was lost in a tragic boating accident this morning. All were lost except for one. You look across your room in dread at your anti-kaiju rifle. You know what you have to do, but you don't know if you have the strength to do it, both literally and figuratively.

Heaving the rifle into your arms, you load a .950 cartridge and begin to waddle towards the door. Your feet make a loud “thud” as you take each 6″ step. You know the intruders hear you. You hope they do, for perhaps they will run and spare the world the suffering that is about to befall it.

You try to set the rifle down, but end up clipping your bedroom door and it is immediately knocked off its hinges by this battering ram in your hands. You attempt to round the corner, bonking the muzzle against the doorframe and adjacent wall across the hall at least 4 times. To your horror, two invaders stand there at the end of the hall.

With a heavy heart, you raise the rifle to your shoulder while making inhuman grunting noises from the strain of attempting some semblance of a shooting position. The burglars simply stare in disbelief, unable to process the situation they are witnessing, as if in a dream. You cannot aim the rifle, as the last time you fired the gun, it turned your $3000 Leupold into a kaleidoscope. You simply hold it at an angle that appears correct and fire.

You are immediately knocked to the floor as if hit by a semi truck going 20 MPH. The shot connected with one of the criminals and it erased him from existence. Even the memories of him have been destroyed and you're wondering why you just shot into an empty hallway. The shot continues to travel through at least 4 houses, a car, and a 10 ton boulder before lodging itself 20 feet into a nearby hill, never to be seen again.

It is at this point, you realize you cannot hear. The surviving burglar can't hear either but he's also on fire from the muzzle blast and is currently vacating your home. You don't care. Your shoulder is dislocated and there is a hole in your brand new AR500 refrigerator. You're crying now. The police arrive and, upon seeing the scene, start laughing. You start crying harder.

Original full reply on Quora

I had to think this through because it posed an interesting question: what is the provably WORST gun for home defense? A .22 single shot rifle is at least small and quick to point. A Barrett M82 is at least going to instantly stop whatever it hits. Even a good old fashioned musket is going to do good damage and won't hurt your ears. No, I wanted to know what the undisputable worst home defense gun in the world is; and I have found it.

This is the .950 JDJ Fat Mac. It is a 100 pound, 5 foot long rifle that shoots a one pound solid brass bullet at 2200 FPS. It is a non-NFA item only because the ATF gave it a sporting exemption as a joke as if anybody is going to hunt with this. This round would be overkill for hunting blue whales.

I would like to paint a picture for you. It's 2AM and you hear a window break in your living room. This is the worst day this could happen, as every single one of your guns was lost in a tragic boating accident this morning. All were lost except for one. You look across your room in dread at your anti-kaiju rifle. You know what you have to do, but you don't know if you have the strength to do it, both literally and figuratively.

Heaving the rifle into your arms, you load a .950 cartridge and begin to waddle towards the door. Your feet make a loud “thud” as you take each 6″ step. You know the intruders hear you. You hope they do, for perhaps they will run and spare the world the suffering that is about to befall it.

You try to set the rifle down, but end up clipping your bedroom door and it is immediately knocked off its hinges by this battering ram in your hands. You attempt to round the corner, bonking the muzzle against the doorframe and adjacent wall across the hall at least 4 times. To your horror, two invaders stand there at the end of the hall.

With a heavy heart, you raise the rifle to your shoulder while making inhuman grunting noises from the strain of attempting some semblance of a shooting position. The burglars simply stare in disbelief, unable to process the situation they are witnessing, as if in a dream. You cannot aim the rifle, as the last time you fired the gun, it turned your $3000 Leopuld into a kaleidoscope. You simply hold it at an angle that appears correct and fire.

You are immediately knocked to the floor as if hit by a semi truck going 20 MPH. The shot connected with one of the criminals and it erased him from existence. Even the memories of him have been destroyed and you're wondering why you just shot into an empty hallway. The shot continues to travel through at least 4 houses, a car, and a 10 ton boulder before lodging itself 20 feet into a nearby hill, never to be seen again.

It is at this point, you realize you cannot hear. The surviving burglar can't hear either but he's also on fire from the muzzle blast and is currently vacating your home. You don't care. Your shoulder is dislocated and there is a hole in your brand new AR500 refrigerator. You're crying now. The police arrive and, upon seeing the scene, start laughing. You start crying harder.

I saw JD Jones at a grocery store in Ohio yesterday. I told him how cool it was to meet him in person, but I didn’t want to be a douche and bother him and ask him for photos or anything.

He said, “Oh, like you’re doing now?”

I was taken aback, and all I could say was “Huh?” but he kept cutting me off and going “huh? huh? huh?” and closing his hand shut in front of my face. I walked away and continued with my shopping, and I heard him chuckle as I walked off. When I came to pay for my stuff up front I saw him trying to walk out the doors with like fifteen Milky Ways in his hands without paying.

The girl at the counter was very nice about it and professional, and was like “Sir, you need to pay for those first.” At first he kept pretending to be tired and not hear her, but eventually turned back around and brought them to the counter.

When she took one of the bars and started scanning it multiple times, he stopped her and told her to scan them each individually “to prevent any electrical infetterence,” and then turned around and winked at me. I don’t even think that’s a word. After she scanned each bar and put them in a bag and started to say the price, he kept interrupting her by yawning really loudly.