Semi automatic rifle made by Ruger.
Chamber pressure is determined by the cartridge, not the rifle.
580 is the newer version of the Mini 14 Ranch, minor engineering changes, improved accuracy, etc.
Good
The Ruger Web site says the Mini-14 Ranch Rifle and the Mini-14 Tactical Rifle, can be used with either the .223 or 5.56mm round: Mini-14 Target Rifles ONLY accept .223 Rem. ammunition. 5.56 NATO cannot be used in this model. Probably due to tighter chambering dimensions for accuracy.
50 USD or so
10 rounds
You rifle appears to have been manufactured in 1983.
NATO 5.56 projectiles are 62 grain, and can be fired through a Mini 14.
This rifle was designed to handle 55gr.bullets of lighter.I do not believe that the heavier 62gr will stabilize with the rate of twist of the mini-14.
$600 - $1000, depending on specifics.
No, the M14 and Ruger Mini-14 are completely different firearms. The Mini-14 was designed for the civilian market as a .223 caliber rifle based on the looks of the M14, which fires the larger 7.62x51mm round and has fully automatic capabilities. They do both however have a gas-operated rotating bolt action.