If you are thinking of starting an online store selling firearms or ammo, your choices are limited to the shopping cart platform you can use. In 2018 Shopify changed their policy on the types of guns (firearms) that can be sold on their system. Even if you have one of the approved ones, they won't let you use their payment processor so you have to use a 3rd party, which they take a fee for each purchase! If you're curious, here is their list. Shopify Acceptable Use Policy.
Lucky for us, we build most of our client's shopping carts in BigCommerce! There are no firearm or ammo restrictions. Contact us to discuss details and we would be happy to help you out! We also can design your logo as seen in the photo below.