It's not the 590's since that serise number Mini 14 does not exist.
New Mini-14 Ranch Rifle
580 Ranch Rifle (early version): Thin barrel, ejector in the bolt stop assembly, scope ring scallops cast into the receiver, buffer system using the recoil spring assembly, new tooling resulting in a slightly different look to the receiver (more rounded edges, etc.)
580 Ranch Rifle (later version)-581: Thicker flanged barrel, ejector in the bolt stop assembly, scope ring scallops cast into the receiver, buffer system using the recoil spring assembly, new tooling resulting in a slightly different look to the receiver (more rounded edges, etc.)
Beginning
Serial Nbr
580-00001--2005--1 in 9
580-15286--2006--1 in 9
580-32382--2007--1 in 9
580-50951--2008--1 in 9
* 580-76276
and 581-00000--2009--1 in 9
* 581-48753--2010--1 in 9
* 581-71056--2011--1 in 9
* 581-95645--2012--1 in 9
* New Mini-14 Ranch Rifles rollmarked with Mini Thirty Rifles beginning in 2009.
Source: http://sunflowerammo.blogspot.com/2012/11/ruger-mini-1430-barrel-twist-rates.html