I'm on rank 2 of the ammo scavenging perk, and I've got like 1k+ on most regular ballistic ammo.
Only one I'm low on is .44, because of Kellog's pistol, and .308, on account of my sniper (but if I get Gun Nut high enough, or find a weapon already with it, I can stick the .50 reciever on it, and then I'll have about 2k ammo).
My sniper ammo actually fluctuates around 200-300 rounds, and I usually find as much ammo as I spend.
The .44 is harder, as I am probably using the .44 revolver wrong, as I have it replacing my Shotgun, and to be honest, I'm not quick/accurate enough at close range to make use of its ammunition.
I only chose it because I didn't have a Combat Shotgun yet, and was fed up with having my Double-Barreled have to be constantly reloaded.
Which also reminds me, my absolutely most favourite weapon so far that I have found, is on my first playthrough, I found a Bottomless Clip Double-Barreled Shotgun, that you could just fire indefinitely.
If it didn't mean I would burn through 100 shells in a minute, I'd have used it just because of how hilarious it was.