It can be a good business, but there are problems.
Start up cost is high if you want to actually make a profit.
You need a place where you can legally Manufacture ammunition. Temp controlled building with some room to test your products for pressure and velocity. Accuracy testing of rifle rounds needs 100yds min.
Machinery to make the ammo. $$$$$$
Powder, brass, bullets and primers. 1 million primers doesn't last a week. Think about that...
Test barrels for pressure and velocity.
Actual firearms for function testing.
A big assed safe (room sized) to safely store them.
Computers
Tools
People to load.
People to QC
People to package
People to keep inventory and ship.
Someone to answer the phone.
At least one sales person.
Good luck getting good people.
You'll need monthly/annual contracts.
Contracts to be supplied with packaging materials, bullets, brass, powder and primers or you can't produce.
It goes way deeper than this, but I listed these just to give you an idea on the basics if you want to produce anything in volume.
Can you manufacture commercial ammunition in your garage? Of course, it's been the startup of many companies like Black Hills.
Do a lot of cost analysis and be realistic about production rates before you decide to jump in.
You need the proper FFL too, don't forget that. Anything over a certain amount is no longer considered a "hobby" when being sold. I don't know what this is but I recall reading it somewhere. Local licenses, etc., and I shouldn't need to tell 'ya this needs to be an LLC.
Then there's storage and a proper magazine that's been inspected by the local fire marshal on top of meeting codes and regulations for that type of business in your area. Are you zoned for it?
Insurance. OMFG insurance. And a lawyer, you need a GOOD idiot and liability statement that will hold up, also you need to know your actual exposure and liability. Find a good lawyer, an NFA lawyer may be a good place to start.
SOP for handling of explosive materials. Grounded workstations? Assume all employees are idiots. Redundant safeties and QC batch testing. ONE bad load in the wrong weapon held by the wrong person can cost you millions. Ever made a mistake reloading?
A small garage setup is one thing and even then you can find yourself sitting on too much powder and primer --one brick of primer IIRC is equivalent to a hand grenade in explosive potential? So a large business doing it is essentially sitting on a bomb if not handled properly.
Due to cost of pressure testing, pretty sure large powder mfg., etc., will pressure test loads for small businesses but not individuals. Not sure if there's a cost or a limit of how many they do or what but I know they do it. That's your biggest hurdle really for small batch/custom handloads.
FWIW, the commercial loading presses look a lot like pill presses and that may be what they are... A spinning drum with dies and cams and presses and pulls shit, really fast, like one blur fast. They're very expensive, very precise and look like a super pain in the ass to maintain but I could be wrong... I seen one guy rig up several Dillon 1050's to a motor and belt assy., all sorts of alarms and shit, and it'd run in his garage automatically. Auto shutdown when it ran out or something went wrong. Looked cool, but it was obviously a pain in the ass and I figure with what he had into it all total, plus time and effort, he could have just bought a commercial one... I bet all he did was load primer tubes and swap those all day long, not to mention unfucking the primer mechanism now and again when it jams due to debris. Wow. NOT the way to go man!
Finding people to buy into a custom load business is hard and then manufacturing enough bulk range ammo on Dillon gear for profit I think is equally hard. I'd keep it a hobby to begin with if I were you, but I'd get the LLC and the insurance for sure if you plan on selling it. Dip your toes, don't jump in. I've thought about this myself but always get talked out of it.