You can still run a room out of your home for the purposes of selling guns with a FFL License. What makes you think you can't? Get firearms instructor certification or certification as a gunsmith and there is no problem. Being a certified gunsmith isn't very difficult.
You may be right. I got out when the rules where changing. At that time, they wanted a dedicated location...but since I was out of the business, I stopped keeping up with the FFL laws.
A few pages back you mentioned not being able to ban dirt and wood for the making of explosives.
If one is a farmer, you have access to the more restricted fertilizers. Farmers put nitrates on their fields. It it not difficult to extract potassium nitrate out of farm soil. Time consuming, but not difficult at all. Potassium nitrate is also the main ingredient in powder stump remover. Sulfur? It is a soil additive that can be purchased by the bag full from garden centers, and sulfur is benign by itself.
Hell, you mix the right (or wrong) pool chemicals, you can make them explode and release toxic gas.
Some fireworks I make require nitrocellulose. Nitro in the name makes it sound dangerous...most brands of PING PONG BALLS are made 100% of it and dissolve very quickly in acetone. Take a ping pong ball and set it on fire. If it burns fast, bright, and leaves little to no ash, it is nitrocellulose. I used to make napalm by dissolving Styrofoam in gasoline to make a thick sticky and very flammable goo.
If they are able to get my firearms, I have the knowledge and ability to make things more dangerous than a semi automatic rifle or handgun.
With firearms, snipers say one shot one kill. With one explosive, one blast can be dozens or hundreds.
Removing firearms may actually make those who want to kill have to improvise more deadly and effective means to get the job done.