For anyone who knows anything about shotshells, in fallout new vegas, why are the only non gun-runner loads "buckshot" and "slugs"; are there just no bird loads in the world of fallout?

In the real world bird loads are the most abundant type of shot
25 bird loads costs about 5$
5 buck loads costs about 5$
and 5 slug loads cots about 5$

so where did all the birdshot go?

I don't think it would be feasible to use birdshot on anything with any DT at all because of the number of pellets in each shell. Moreover, I doubt a bird load would be a real deterrent to any soft target aggressors found in FNV, as you'd likely have to be at point blank range to do any permanent damage--and even then, not necessarily a fatal wound--to someone irl. From a gameplay perspective, the only real use I could see would be as a cheap alternative ammo like the .223 or .22LR plinking ammo that's already in the game presumably to be used against small pests like rats or coyotes, or to be broken down at reloading benches.

First off, like youve said .22s can damage people, so even the smallest of loads should.
2nd, I guess its dismissible because in fallout .357s only take off a 3rd of an unarmored man's heath, so... yeaaah.
and third, DT is a load, if i shot a man with a vest on his chest at point black with 12 gauge #8 bird, he would have to weigh 300lbs not to fall on his ass, and he would be lucky to have his ribs in tact.

Either way, BB guns can damage people in fallout for christ sakes.

True, but .22lr has pretty limited use in the game. Once you get a better pistol, you're not using the .22 anymore. The cheapo plinking ammo is okay for the .22 smg I guess, just as a more cost effective way to chew through the rounds in those fat drums. Anyway, in real world ballistics it's fathomable that a well-placed .22 would penetrate at a much farther range and would actually drop a guy if not kill him outright, whereas birdshot is probably not getting much more than skin deep at any kinda distance. You'd feel the sting, you'd prolly get knocked on ya ass, but you could keep going.

20ga ammo is already among the cheapest in the game, and 12 ga isn't really expensive either. Consider also that all shotshells have 7 pellets in NV, except the 3/0 and 4/0, and you can still shoot lightly armored muhfuhs in the head from less than 10 feet away and not even take away a third of their health, so (and I have no idea how many BBs are in a single birdshot shell) what would having many more pellets doing way less damage actually accomplish? They'd have to rework the whole system to make it work, and maybe they actually should for the next game, but whatevs. It is what it is.Like you said, .357s only do a moderate amount of damage and you can pick off someone with a BB gun so they're not exactly going for realism.

yes, but like ive said, the .17 bb gun moving 800fps does damage.
Why not 16 .25s moving at 1250fps? (#8 bird)

re-read your comment:
are you familiar with bird loads?, they dont sling sand sized projectiles, although small they cause organ damage and think of it this way.

Do you think that if someone shot you with 12 gauge #8 bird from 20 yards (improved cylinder choke) you would pick out the birdshot with a tweezer?