How do the GMs out there handle it?

Determined by the ammo's availability rating, population size, anything else?

Is the target # influenced by the amount wanted, # of successes go from individual rounds, to clips, to crates?

Unless you want some rather exotic ammo (Exitus rounds and vortex grenades spring to mind), that's very simple: Enough.

Every weapon you buy automatically comes with a standard ammo supply pretty much as large as you need it to be. If you want a different type, you need to Acquire it seperately for the number of men you want to outfit it - meaning you generally make an Acquisition test with the rarity and the scale as modifiers. If you succeed, you've managed to Acquire a source of ammunition that will most likely last you a lifetime, unless you unduly strain it in which case the GM may call for an Upkeep Test.

In the operation that i am in we have a munitutiorium where the ammo is stored.

When someone purchases or acquires a weapon they get a "Personal supply of basic ammunition" be it laz cartridges or bolter rounds.

If they see the need for specialty ammunition we attempt to find it and when it is acquired they receive a "Personal supply of specialty ammunition"

As for using your profit factor in acquisition of said ammo;

What we do is allow the "Captain" (Person in charge of the dynasty or acting person in charge) to have access to our Profit Factor in order to make acquisitions that much easier.

My personal experience with ammo is to make sure that you are prepared with as many things as possible, IE: Tempest bolt shells, Psy-cannon bolts, Inferno Shells and basic bolter rounds for my storm bolter

Thank you for the feedback.

We're just now starting to try and get some of the exotic ammo and I managed to get my hands on an Angelus, which has ammo nearing super exotic and I don't know what an appropriate roll would be to get Astartes ammo for it.

For Astartes ammo, I'd say that it is either Very or Extremely Rare, given there are only a million or so Space Marines out there, and that means someone will have had to have smuggled some away from a Chapter.

Probably Extremely Rare, considering I'd peg it as the second-most rare ammunition type after Exitus ammo.

Further, I'd probably require frequent Upkeep tests - people selling Astartes bolts on the black market may not have too great a life expectancy.

*Hugs his Space Wolf Captain*

Or make friends with a (somewhat friendly) Space Marine >.>

Or get friendly with one of the Tech-Overseers at the production facility. Production over-runs are ***** to deal with, arn't they?

Just had a thought, try and find, either through exploration and/or researching databases the location of a Space Battle where there is a Space Marine Vessel. Go through the motions of acquiring "The Rights of Salvage" and viola! Adeptus Astartes Equipment and Weapons and all the Astartes ammo you'll need for a loooonng time, don't think you'd get the rights to keep a Astartes ship though, that does depend on the GM.

I'd personally say no to getting legal rights to salvaging a Battle Barge (assuming there even is one around Calixis/Koronus), since it belongs to the Chapter in question, and as such is not for others to give away. If you, as a GM, want the PCs to piss off said Chapter, however, go ahead and let them salvage it illegally That should prove fun!

For normal ammo, I just assume all my players always have 3 clips for each weapon. And if they run out, they have more in the starship or guncutter.