Very interested in starting my own shot gun shell wholesale business. Anyone on AR15 done this before? What do I need to know. No guns for a while and not interested in other shooting related products right know. I realize this is not the time to open up, looking at 24 month timeline. Wondering about insurance, selecting manufacturers, finding retailers, advertising, profit margins, etc.

With the current political administration and their utter contempt for anything firearm related, I wouldn't even think about getting into any business related to firearms.
As to manufacturers, they all will be glad to sell to you - if you place large enough orders.

Investigate the legal aspects of your intended corporate structure: sole proprietor company, corporation, or LLC. LLC is best for protecting your non-business assets from civil suits. You can be a single member LLC, or have partners of varying levels. Understand the tax ramifications for each type of business structure. LLC is what I did when I had my photography business. Understand the business license structure of your state, county, and city and the state tax structure, getting your EIN number, setting up workers compensation plan (if you expect to have employees), employment tax(social security etc), vehicle, office, warehouse, etc. Insurance is a must and plenty of it. If you sent a case of ammo and the shipping box rips dumping boxes on someones foot......lawsuit! If you have a wreck while transporting ammo (business function) your regular car insurance will not cover you without a rider for business use of vehicle and when people find out you are a business the sore back/neck becomes critical and too late to think about getting insurance. You will need a lawyer to be your representative for point of contact for business legal correspondence, contracts, etc. I would suggest going to Legalzoom website to study the process or contact a friend that knows a business lawyer. I used Legalzoom for my LLC. Covering your a$$ is complicated and necessary.

JB

Inventory and customers.

Somewhat joking. Before you dive in, you’ll need some idea of your costs, before you can formulate a sell price, to calculate your GPM.

I’d put some time in talking with suppliers first. I think you’ll be surprised by the ‘buy in’ amounts, in both price and qty levels.

Consult with an attorney in your area

A frontal lobotomy. Bless the hearts of those who do it.

The gentleman that I buy my reloading supplies from likely got into the business to support his habit but I’d hate to try and start a business now selling ammunition or reloading supplies.

I would encourage you to research it. It would be really tough going against the big boys. Load your shells and go to big shoots and hand out samples and give your reasons they should use your shells. You will have to beat the others with either quality or price hopefully both.
The trouble with manufacturing ls the machinery cost. if you have enough money to start you probably could retire on it with no risks. Getting start up loans from a bank will be tough,as they will only loan a small percentage of what you need, you will have to have a large chunk of skin in the game. I sit on a bank board and examine loans all the time. Banks like to loan money if there is real estate involved, construction loans are the most difficult to get.
Winchester,Federal,Fiocchi, Rio,Remington ?,have been around forever they are not going away.