I assume you added the new ammo to the formlist for that weapon? It's probably in the first "slot" then, and is being considered the "default" ammo type for that weapon.
rofl, okay, never really messed with ammo, normally just messed with interiors, didnt know that mattered =P it is definatly in the first slot, ill fix it then report back if it doesnt change.
didnt realize, but now that i think about it, i was finding A LOT of it pretty much everywhere.