@AlwaysLearning
To give some more context to the last handful of posts, again it's a bit dry but stick with it.
Throughout the history of firearms, there has been endless iterative attempts to find perfect calibers, this has resulted for better or worse in a selection exponentially bigger than what would be needed to cover all situations at all times. Partly driven by advances in technology but mostly driven by the need to tinker and somewhat driven by marketing. There are many calibers that are very similar to each other and many that start with a hiss and roar but become redundant due to having a ballistic twin with better marketing, (think Betamax vs VHS).
An ammunition manufacturers production lines can produce various different calibers but there is down time switching from one caliber to another, as such they tend to perform more runs of the more popular calibers, while the less popular calibers or orphan calibers get less of a look in. The upshot of this is that some calibers are as easy to find as parts for a Toyota corolla, while other calibers will have unreliable supply.
Without going too deeply into politics, depending on the presidency of the US, the citizens in the land of the free can have greater propensity to stockpile ammunition. This results in periodic cycles of less reliable availability of ammunition in countries far from there.
Some calibers that I know of that have more reliable supply are .308, .223, 6.5Creedmore, .270
.243 and 7mm08 & 6.5 Grendel are in the camp of less reliable during shortages. 6.5Cr was also hard to feed at the last great shortage, but it is much more established now.
If you are on the fence in the 308 vs .243 debate, 6.5Cr is a good middle ground and should be as easy to obtain as anything else for the predictable forseeable.
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