Another rules question: How does acquisition of special ammunition work?

Pg. 113 of the RT says that a weapon gets an infinite supply of default weapon stored on the ship, they just have to declare how much they are bringing with them on any given expedition.

Does special ammunition work the same way?

If so, what scale should I use? Negligible doesn't feel right for a lifetime supply of ammo, even if it is only for one person.

Negligible sounds right unless you are supplying ammo for a larger number of people I wouldn't worry about it.

For instance in my campaign I play the master-at-arms, and I have to supply our special forces unit with equipment. Ammo for one gun regardless of type is negligible. If i am buying a supply of tracer rounds for 30 guys that's different so I adjust the modifier accordingly.

Also, I don't know how much ammo you expend, but my guess is in the grand scheme of things its pretty negligible unless you are just pissing ammo away firing at high rof for no reason.

You could simply use the existing quantity modifiers:

Amputator Shells are Extremely Rare; I want to acquire 10,000 rounds so a modifier of (Vast, 10,000 -30) is assessed. thats -60 already. Booyah. Have them keep track of their usage.

By the rules the rarity given is for an infinite supply. This works out just fine for most games. If you are playing it where the RT and group does not have nearly the wealth level represented in the books, you would need to rewrite many of the availability ratings. In addition I submit to you that firing a single macrocannon shell from one of the many guns your ship is liekly to have would cost more than a heaping pile of special ammo for personnel weapons. So you might want to keep track of that as well.

You could also say that the acquisition roll includes a contact to get more ammo if needed. So the player doesn't actually get an unending supply of ammunition, he gets enough to hold him over to the next supply run and a name of a guy who'll sell him more of them when needed. (Without a roll or PF impact)

That way you might require upkeep rolls for highly special ammunition if the crew is on an unplanned extended run for some reason, the ammo will replenish at the next port.

I stole and butchered some rules from Deathwatch. You have three choices in your supply: One endeavour (About four or five sessions for my games), one meta-endeavour (Usually about three to four endeavours of varying size) or an entire campaign.

You get +20 for the first, +0 for the second, -30 for the last. That's how long you have access to the special ammunition for, in a hand-waved "You bought a crate/a shipping container/a cargo hold full of them, and find yourself coming to the dregs of the container just as your vessel catches sight of your implacable foe..." sort of way. So far it's worked out pretty well. You can also make them test for Upkeep if they use a lot really quickly.