One of two things needs to happen here... We need a way to get to our last posts easier or I need to log in more.
It's been said the best rifle for after the theoretical SHTF is what you have on hand when it happens. If you have nothing when that happens because you were saving up to buy something out of Aliens, well, good intentions won't keep the MZB out of the tomatoes. If you believe that the Zombies are just over the hill (i.e. Imminent), purchase something less than what you want NOW, with ammo in quantity and whatever else. Make due with that until either you have saved up enough to buy the Phaser/Disruptor or the Zombies are at the front gate. If the better/more desireable firearm does make it in the door before the Zombies eat the last postal worker, the lesser firearm can either be sold (probably for at least as much as paid for it) or kept on for other family members who would have need of it.
K, ammo. I do admit that storefront locations that sell firearms/ammo will be one of the first stops for the overly aggressive, no food stored types. Probably right after the beer store. Problem with that is that any switched on police department would make that stop first, then the station with the trunk load of "for safety during this crisis" firearms and ammo. All the second wave should find is a store full of cammies, cleaning kits, fishing lures, targets and empty sales racks and ammo shelves. Sure, there are alot of hunters out there. I know more than a few who have a partial box of ammo on hand most times. One round to confirm zero, one round to drop Bambi. Box of 20 rounds lasts 10 years. To boot, my local Cdn Tire has limited ammo on hand (usually not more than 5 boxes of the large bore), and no firearms, just air rifles/paintball markers.
For those who have never seen x39 (and others) in bulk...those of us who have often order it via this internet thing. It gets delivered to our door, or at least to a location which is served by these delivery services, which may or may not be where we live. I believe my last order arrived via CANPAR, in a green wooden crate sealed with a fibre strap. The crate had the explosives sticker removed and a "Comsumer Commodity" label added. It shouldn't take a casual observer much to figure out what the delivery guy was carrying as it was stone heavy (actually a case of 7.62x25).
The US Military changed from 7.62 to 5.56, yes. As did the rest of NATO (eventually) becuase of a shift in military tactics. The thought was that a smaller round would wound a person rather than kill them, thus making them a burden on the supply system and remove more people from the battle (a dead soldier is a dead soldier whereas a wounded soldier needs two to four guys to carry him off the field). The side benefit of more ammo was found to be less beneficial than thought. It was found that soldiers (now all armed with automatic weapons of various ability) would tend to spray and pray more often and run out of ammo in less time than they might with aimed shots of larger calibre, with fewer enemy casualties.
This, is my .02
That and $1.75 should get you a coffee.