Here's my 2¢ worth on some of the weapons and ammo related questions.

It's important to realize that our heroes don't need major amounts of ammo; one lucky find could easily provide them with everything they need for years to come. Consider that, at most, the humans can field 1) 2 50 caliber machineguns, 2) 1 Minigun, 3) 1-2 SAWs, 4) 10-15 scoped rifles (the old Guardians weapons) and 5) maybe 50 M-16s. Key calibers are 50 cal, 7.62mm, 5.56mm, and 9mm for military/police pistols and submachineguns. 100,000 rounds of ammo would refill their ammo bunkers to overflowing.

I've seen one Army cargo truck, half-loaded, deliver 500,000 rounds of mixed ammo to a range; fully loaded that one truck could have carried over a million rounds in it. My old company's ammo bunker had over 1 million rounds of small arms in it, and as a bonus it also had land mines, hand grenades, C-4 and anti-tank rockets in it. A single cargo container, enroute to Iraq of Afghanistan through an LA port could have 10 million rounds of ammo in it.

Quote Originally Posted by scbubba View Post
...So the military locations. Other than the base that Michael mentioned (Navy base, right) and the National Guard base (which has long since been empties), we don't know the state of any other potential military supply locations. I'm guessing that Michael and Co haven't made a visit to any of these military locations in Season 4 but I wonder what they might find if they did...
There is a lot of potential for scavanging for ammo around LA. Among military bases there is the Long Beach Navy Base (which exists only in the WA Universe, the real one closed in the 90s), there is the large National Guard base at Los Alamitos and there are at least a dozen armories like the one in Bell. Further afield there are major Marine Bases at Twentynine Palms and Camp Pendelton, major navy installations all around San Diego and a half-dozen military air bases. There are also major container ports at San Pedro and Long Beach.

Quote Originally Posted by scbubba View Post
...As for access to reloading supplies, powder might be the easiest of the materials to come up with. Brass could be in decent supply depending on how much of their own they have saved. The primers are going to be the kicker there. During this year's ammo shortage, primers were one of the 1st reloading materials that I saw go into short supply. And given Cali's general low ownership of firearms (compared to most of the rest of the US) I would think that the general availability of primers would be really low in May 2009 in LA....
Let's not forget the problem of getting lead for bullets. You can make bullets out of brass or steel, but it's a lot harder than doing so from lead. These days lead isn't used for much except for making bullets, and over the last ten years most of the US lead smelting foundaries closed (the last one in the US closed just last month). For years most of the lead used for making commercial ammo has been imported from China. Once the stocks on store shelves is gone, the supply is gone.

Quote Originally Posted by scbubba View Post
...To the best of my knowledge, the US military doesn't do much if any reloading (Cabbage Patch, any info on this?) so I would think that there wouldn't be a supply of primers for any caliber available at any of the military locations...
As far as I know the US Military doesn't do any re-loading. Spent brass is shipped back to the ammo plants, where it is melted down and recast into new shell casings.

Quote Originally Posted by Unit9014 View Post
...Here is an awesome article I remembered reading a while back about groups in Africa creating their own shotguns and shotgun shells and using caps from kids cap guns as the primer. In reality you can use anything that makes a spark as a primer. Works good enough for a single or double barrel type shotgun, but I don't think I would trust it in anything where the ammo is 'moving' like a semiauto or pump gun...
It's amazing what a skilled craftsman can do! In places like Afghanistan and the Philippines there are people who can build you a workable copy of a Lee-Enfield rifle or a Colt 45 Automatic out of scrap metal, using just hand tools, and without electricity. The guns they make aren't pretty, they are heavier than the originals and I would be nervous about firing one myself, but they work. Given all of his advantages, Datu could probably build even better weapons if they were needed.