I really want to make a gun mod but I am unsure how to make a magazine with a shooting gun. Also with a GUI telling you how many bullets you have left. Can someone teach me how please? I am willing to reward whoever helps me successfully make a gun mod (Only 1 gun is needed, I can figure it out on my own for other guns).

As long as you know some basic java, and know how to create items.. Then it should be pretty self-explanatory, just look the bow for reference.

Well Lambda that's true, however not enough leads for Skullmassarce to work with, only half.

 

So following Lambda's advice see some tutorials on making items and registering them (and configuring the JSONs for the textures and whatnot)

 

once you have that done, you will want to look at some vanilla code aka like Lambda mentioned the bow (for the right-click to shoot function)

 

Then once you have the "gun" functioning with "ammo" which at this point will act like the bow (consume ammo from the inventory) now it sounds like you want a "reload" aka extra ammo in inventory but gun can be loaded and shoot as long as it is loaded.

 

If that is the case you will have to look into capabilities (so you can store extra data)

 

after once that is all setup it will be looking into other things (key presses for force reload, if they can reload, auto reload if gun is empty and ammo is ready)

 

EDIT:

 

but it depends on how you WANT it to work, you could have the ammo just have durability and have them limited to stackSize of "1" and the durability is the ammo in the mag/clip. But the effects of that would more or less be no reload (just burn through the clips, classic and 2016 DOOM anyone?)

For starter I recommend looking at bow and how it uses arrows from inventory. Try to make a variation of the bow but make it a pistol model + bullet arrows. Once you figured all that then I recommend figuring it out how to do a gui overlay. Then you can keep expanding on the pistol bow until you get what you want.