So because I often was short of ammo during Ram Raider and Rush Hour and I noticed that Riding Shotgun can give you a lot of ammo, I looked into what missions can actually give you what ammo.

You start with no ammo in 2006, but you get some during the first missions:

• You can pick up a F70 in the first mission (The Mexican) and about 300 ammo for it, some of which you'll probably use to kill people
• The next mission (Tailgate) will probably use up a lot of it shooting the car, however after finishing the mission (after the cutscene) you get 50 ammo for the F70 (this also applies if you have used up all your ammo) and 8/8 ammo for the Gangster Pistol
• After finishing Guardian Angels you get 40/40 ammo for the SF10 (on job done)

After that you can either do the first Ram Raider mission or go directly to Riding Shotgun. The idea is to do Riding Shotgun before Ram Raider, Rush Hour and Gauntlet because I noticed it seems to give you a lot of ammo, which you can then use for those missions.

When I tested Riding Shotgun I was at first unsure why sometimes I seemed to get different amounts of ammo and sometimes even basicially none. After playing through the lovely autoscroller many times, I noticed that it seems to depend on the ammo you currently have for each weapon, more specificially the ammo you have in reserve, not in the current clip. It seems to give you <Ammo in reserve> ¤ <Magazine Size> for each weapon (and also fills up the current clip). It caps out at the maximum ammo each weapon can have, although if you do get that it should certainly be enough for the rest of the route.

I've also seen runs/done runs where you have a lot of ammo later, but I'm not exactly sure where that was coming from. It didn't seem to be there after Riding Shotgun, but I've seen it at Candy. I've done a run with the Guardian Angels -> Riding Shotgun -> etc. route and I didn't seem to get any additional ammo anywhere else (except the RPG and Minigun), but maybe it depends on what you already have or the mission order somehow.

If you do Riding Shotgun first you can get a lot of F70 or SF 10 ammo, both of which seem to be able to kill the helicopter in the last mission roughly as well as the Aust PUP (which you otherwise would have a lot of ammo of and possibly don't with the new route).

Here is the data from the tests I performed (loading from a safe after Guardian Angels and then shooting away different amounts of ammo before Riding Shotgun):

32/18 -> 50/900 50/0 -> 50/0 50/1 -> 50/50 34/18 -> 50/900 15/2 -> 50/100 50/3 -> 50/150 50/68 -> 50/2000 0/0 -> 50/0 13/0 -> 50/0 24/0 -> 50/0 3/22 -> 50/1100

39/40 -> 40/1200 1/40 -> 40/1200 40/39 -> 40/1200 0/0 -> 40/0 40/11 -> 40/440

8/8 -> 8/64 8/0 -> 8/0

Ok, so I found that you get the "AK" (AUST PUP) on the job done of Gauntlet (30/30 ammo). So that's probably where you then got the 900 (30¤30) AK ammo from, since you did Riding Shotgun directly after it (and me as well before changing the mission order). You also seemed to have picked up some machine gun ammo from the last enemies during Gauntlet, so that's probably where you got the other ammo from despite having depleted all of it before.

So I'm not sure if the AK is any better than the other machine guns, but the other ones seem to work well enough. And you use the Minigun for the last missions anyway, except for shooting down the helicopter in the last mission. In any case, having the ammo from Riding Shotgun earlier is probably faster anyway, even if the AK was better for shooting down the heli and stuff.