https://ruger-docs.s3.amazonaws.com/_manuals/mini.pdfThe RUGER® MINI-14® RANCH rifles are offered in two calibers: the .223 Remington (5.56mm) cartridge and the 6.8mm Remington SPC cartridge. The Target Model uses .223 Remington cartridges only.
RUGER® MINI THIRTY® rifles are 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 Mini-14 Ranch and Mini Thirty Rifles are designed to use either standardized
U.S. military, or factory loaded sporting cartridges manufactured in accordance
with U.S. industry practice. Always be careful to ensure you are using the correct
ammunition for your rifle.