You are already paying for taxes on ammo. The US corporate tax is the highest in the world - average 39%. Plus franchise taxes, property taxes, etc. All added in which you pay when you buy ammo. After those taxes are added in, you pay sales tax.
Right now, some states & cities are considering an excise tax on ammo. Similar to the excise taxes on alchohol & Tobacco. This should be a concern for all. One more reason all of us who enjoy the shooting sports need to be vigilant and informed about what is happening at the statehouse, county, & city hall.