Go to pip boy and press what number you want to assign the item to then click the item 1 then 3-8. Slot two is already used and can not be reassigned as far as I can tell yet.
Oh man, I was using number 2 in the first place. Forgot it was the ammo subtype switch (what a bad assignment though! I hope Obsidian changes this to a separate assignable button)
I like being able to go 1,2,3,4 for quick access items, and X to ammo type switching.
Thanks for the info
@Beknatok & Troyniss - Thanks for the info, will try the remap when I get home. Appreciate it.