Haha, yeah I'm talking about the Bert's in the world! Good analogy.
I'm also saying that .223 and 7.62x39 & maybe x51 are typically fired from a semi/auto with hi-capacity magazines. In the hands of a well-trained effective and efficient shooter, a 30 rd magazine of 308 is a formidable threat to 30 people.
That same weapon, no let's say AR since they're so popular, in the hands of a lot of american firearms owners isn't a threat to a cow. They will rely on the speed of the action and their magazine capacity instead of accurate controlled fire. They may use 20 rds when 1 will do. Look at newsfootage from any real world crisis scenario and you will see spray and pray, not aim and squeeze. A scared human unfamiliar with their firearm will also drop it with a jam, instead of executing a clearing procedure, or attempt to cycle on a blockage. Seen a few blown up aks in the sand.
That said, A LOT more milspec ammo (5.56, 7.62) will be used up ineffectively early on after an EOTWAWKI scenario. I predict without resupply, it will be used up faster than any other caliber until the more fragile actions begin to fail due to abnormal use and poor maintenance.
Not only that, because of manufacturing, and fear, many folks own 1,000s of rounds for them, most likely not in a weatherproof, fireproof container. A nice flood renders a lot of ammo unreliable, especially in gas-operated weapons. Milspec ammo can come from a variety of manufacturers many of which do not meet the same qc as US made. So you stumble across that ammo can full of greek milsurp ball, so you load up. You might get unreliable feed, blockage or worse. Entropy dictates that the more complex a system the more likely it is to fail. Alot of milspec weapons are made to high tolerances with full knowledge that it takes a trained Ironglow Jr (armorer) to maintain and repair them in combat use (survival use).
Now take 30-30, most likely fired in a 6 rd capacity lever gun, or a 30-06, in a 4 shot bolt gun. Probably in the hands of a hunter who is used to placing a single kill shot. He may be able to accomplish in 2 or 3 shots, what another guy needs a full 30 rd magazine to accomplish. They may not be found in pallet quantities (maybe the 30-06 milsurp stuff), but they won't be used as fast I'm guessing.
I also suspect .22 will be the last to go; more rounds spent on defense than hunting in the early days, so folks with the option will opt for their big boomer and save .22 for later.
Just trying to think how it'll go down.