interesting... I've never messed with the guns... but I wonder about the ammo stack sizes...
from the
wiki:
Quivers and Bolts
Please note that bolts are assigned to a squad, not to individual dwarves. If you have a squad of 10 marksdwarves, you need to assign at least 250 bolts to the squad. 500 is better.
Quivers can hold between 25 and 49 bolts, and dwarves will pick up multiple stacks if necessary to reach a number in this range. In other words, dwarves will continue picking up stacks of bolts until they've got at least 25 in their quiver (or they run out of squad-assigned bolt stacks). Bolt stacks are collected in last-in-first-out order (LIFO); that is, dwarves will always go for the newest bolts in your fortress, even if there is an ammo stockpile three steps away from them. Each squad with marksdwarves must be assigned ammo; as they deplete it, Dwarf Fortress will automatically add additional ammo to the squad if there is some in the fortress, again following the principle of LIFO.
what stack sizes are you able to make of bullets?
If they are only 50+ then try this:
target a unit with 'v' then in dfhack console type:
createitems AMMO:ITEM_AMMO_BULLET INORGANIC:BRONZE 50
reduce the number by 1 and make another and another, keep checking the military screen to see if they show up... tell me what number you have to get below for them to pick up the stack... On my end I'll start editing down all the reactions... all I'm seeing here are 50 and 100 stacks... and well a quiver wont hold 50 stack according to the web... let me know what you end up at and I'll have a raw edit for you for the future so you can save your fort.