My 582 Mini-30 manual mentions nothing about steel cased ammo directly. I will post the pertinent information from page (11) of my manual below for comparison. I left out the pretty pictures. I shoot steel cased through mine without issue. I have read where some have problems with it though and I also read not to shoot brass case immediately after steel cased unless the bore and chamber has been cleaned.
AMMUNITION
RUGER®MINI THIRTY RIFLESare chambered for the 7.62 x 39mm
cartridge, and can use either standard U.S. military or factory loaded sporting 7.62
x 39mm cartridges manufactured in accordance with U.S. industry practice. Do
not attempt to use any other cartridges in this rifle, even though "7.62mm" may
appear in their names (i.e., 7.62 x 51mm NATO [.308 Winchester]; 7.62 Tokarev;
7.62 x 54 Rimmed Russian, etc.). The only correct ammunition for the Ruger Mini
Thirty is the 7.62 x 39mm. The use of corrosively primed ammunition is not
recommended, See "Ammunition Notice" & "Warning - Ammunition,"
AMMUNITION (CARTRIDGES) NOTICE
WE SPECIFICALLY DISCLAIM RESPONSIBILITY FOR ANY DAMAGE OR
INJURY WHATSOEVER OCCURRING IN CONNECTION WITH, OR AS
THE RESULT OF, THE USE IN RUGER FIREARMS OF FAULTY, OR NON
STANDARD, OR "REMANUFACTURED" OR HAND LOADED (RELOADED)
AMMUNITION, OR OF CARTRIDGES OTHER THAN THOSE FOR WHICH
THE FIREARM WAS ORIGINALLY CHAMBERED.