Depend on ammo type, some gives more than other as in an exchange rate has not calculated it but it looks like its related with price. I note that shotgun shell has high value, sniper rifle ammo is probably higher, 44 also have a high value, 10mm are cheap and 5mm minigun ammo is very cheap. And you have losses if you transformed the 1000 5.56 to shotgun shells I guess you would get less than 1000.
And the exchange rate is not level or skill based.