When the SHTF there isn’t going to be any ammo available except what you have or you can make. Hoping to resupply from someone else is more like wishful thinking than a plan. If you are going to wish upon a star for resupply what do you think is going to be more common, .233/5.56 or .308/7.62?
That way, when the zombies get to us, at least there will be less of them.
Mosins are great guns. Don't count them out to hand out or trade. They are a force multiplier if you can arm your neighbors.
I have a good supply of each, 5000+ 5.56 / 7.62.
Not to mention my supply of 9mm, .45acp,.22lr and 12 gauge.
The simple fact of the matter is, 6.5 or 6.8 will be totally unavailable, and the 7.62X39 will only be moderately more available.