Probably 1.0-1.5 MOA, depending on WHICH Ruger rifle.
Ruger's web site has extensive sn data.
Yes.
If the ruger site comes back up, you can check there sn database
Not currently cataloged.
100-1000 USD depending on specifics
The difference between 6mm and 1/4 inch is very small in terms of measurement accuracy and precision. 6mm is slightly larger than 1/4 inch, but the difference is minimal and may not be noticeable in most practical applications. Both measurements are precise and accurate for most everyday purposes.
1-1.5 MOA with the right loads
580 is the newer version of the Mini 14 Ranch, minor engineering changes, improved accuracy, etc.
22-250, 220 Swift, 243, 6mm Rem, 25-06, 308. Other versions of the 77 were in MANY other calibers.
6mm is equal to a 2 gauge.
6mm = 6/1 mm.
4mm-6mm in inches = -2