You can grind 10 of these in an industrial grinder and get

10 metal ingots, 10 gunpowder and get this: 20 simple bullets even though it takes 10 simple bullets to craft 10 shotgun ammo on mobile

Bonus: You can also grind the 20 simple bullets that the grinder gave you and get 10 additional metal ingots and 20 additional gunpowder

Then you can basically duplicate shotgun ammo

I tried this once and ended up with 10000 shotgun ammo