What are

Cases from ammo (do you need these to make new ammo?)

Powder, Rifle
Primer, Small Pistol
Primer, Small Rifle

These weren't in F3 and im a little confused

Thanks!

They're components for creating your own ammo with a reloading bench. Repair skill is required.

Cases are ammo casing.

like a 9Mm casing.

Powder is what makes the bullet go.
Bullets are made of lead.
Primers set the powder in the case off, propelling the bullet to where its aimed at.

9MM casing +
Small pistol primer +
Lead+
Small pistol powder =
9MM bullet.

Easiest way to get them is to break down other bullets from the reloading bench.
on occasion you can find merchants that have those parts though. i know chet had smll pistol primers once.

they werent in f3 because f3 didnt have ammo reloading.

To get into a little more detail, http://static.howstuffworks.com/gif/machine-gun-bullet.gif. ^_^

The cases are empty shell cases, which you need (along with primers, powder and lead to reload your own ammo. This is all completely new from Fallout 3..

some times some shops (shops random inv?) sell things like a case of shells, a jar of X powder and primers.

Gun Runners shop is a great place to buy and sell things. The shop has PLENTY of caps and lots of guns and ammo making goodies.

What I don't understand is what is the #s next to the names are, for example "Breakdown 20 Ga. (18)", when it doesn't correspond with the amount of ammo or a gun I have. The powder #, e.g. "Powder, Pistol (18) will always match the breakdown #, and the hull/case and primer are always 1, but the powder and the lead change. So this is simply the ratio? Breaking down 1 20 gauge bullet gives me 26 lead, 18 powder, and a Hull and primer? Yes I think I answered my own question. Thanks for listening.