I had a 188 series Mini- it was one with a 1 in 7 twist barrel, there was a short period when Ruger changed the Mini to that twist...
Ruger told me on the phone that Mini's were introduced with the 1-7" twist and were all 5.56 chambered, and 1-7". This was before the Target models came out so I don't know if they have changed the twist or chambers since then.
It's easy to check the twist rate with a cleaning rod. Make a mark on the rod with a sharpie at the muzzle and then pull it out while watching the mark rotate with the rod to make a full revolution. Make another mark on the rod when it makes the full turn and measure the length between the marks. All of the pre target models were 1-7".