"Corrosive" primers contain either mercurial components (rare) or Potassium Chlorate as part of the chemical makeup. Many older surplus or commercial loads have this kind of priming. Modern primers contain lead styphnate, and will not cause immediate rusting or "corrosion."
If you stay away from "bargain" ammunition, you are off to a good start. U.S. government loaded ammo up to 1946 for service loads and several years later for match ammo was corrosive, except for carbine ammo, which was never loaded with corrosive primers.
Many of these older loads and some modern ones from Europe and other continents contain corrosive primers. Somebody could write a large book on all of the variations.
To be safe, either load your own with all new components, or buy U.S. brands or imported brands marked non-corrosive primed.
But, just to make certain, buy only premium bore cleaner and thoroughly clean your weapon as soon after firing as possible.
If you ever HAVE to fire corrosive ammo, you must clean you weapon immediately, then do it all over again for a total of three days after firing to be certain. Corrosive ammo is best cleaned up after with ammonia solvents like G.I. WW-II solvent or the old Ordnance Corps formula found in older gunsmithing books.
[This message has been edited by John Lawson (edited November 14, 1999).]