Ruger's mag lockup / release parts had geometry changes over the years (different number series), so what works for one person may not work for another. You should TEST to see what works in yours before you invest. Test each mag for solid lockup, no bolt drag on the feed lips, and bolt lock-back on an empty mag. Also look for good metal forming, smooth follower travel, and follower engagement on the bolt lock. Pull the bolt back, and when it stops, drop the mag. ALL the Mason's (and 15% of the USAs I tried) failed to lock the bolt, and the bolt simply jammed on the follower and slammed home when I pulled the mag out. These mags are junk.
Also, be aware that companies like PMI, USA, and Mason mags differ in quality depending on when they were made. My mini works well with most of the USAs I've tried, but others hate them. The 2 Masons I have are worthless POS, with the crappiest soft metal floor plates and followers I've seen and no bolt lock-back -- but others seem to love them. Early PMIs were wonderful, but the newer ones seem to have softer metal and the feed lips deform, so I wouldn't touch one without testing, but my old SS PMI is wonderful. Rugers are clearly the best, but the prices are insane for 20s and 30s. The newer ProMags look like OEM quality, and if they start offering 20's I'll be a buyer. Look over at
http://www.perfectunion.com/forums/show ... eadid=1087 (if the thread is still there) for other opinions on other mags. Perfect Union is the site for Mini-14 fans.
I was working on a comparison matrix of different mags (mostly based on geometric differences). This is what I wrote for general impressions on mags I know (sorry, it repeats some of the same info above):
Ruger: OEM mags consistently reliable; high quality suitable for LE or Mil. use. Ruger 5-rds drop free.
PMI (aka Precision) :Older mags appear to be near Ruger in quality, many new mags near worthless due to soft feed lips which bend easily
Pro-Mag: New mfg 10-rd appear excellent, near OEM quality. (Apparently working to get a Ruger OEM contract.) Best new mfg I've seen.
USA: Some USA mags appear to be good quality, reliable & fully functional, and but other reports suggest they made a lot of bad ones also. Confirm fit and operation on individual rifle.
Masen (old): Older mags have poor follower/lockup geometry, no bolt hold lock-back on last shot, and soft metal (esp. floorplate). Newer mags (esp. 10-rd) have much better reputation.
Hope this helps. YMMV.
-- cw