Mine sucks...........it's loose and doesn't feed very well. Unless, the front part of the mag is held up tight. Still can't believe they get $175 for these stamped out accoutrements. The gun does shoot very well though 
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
For the cost of less than 2 factory Sako mags, you can get a conversion from KRG that'll allow you to run AICS mags in your TRG. I'm not sure they're a vendor so I won't post a link but use your googlefu. Well worth it, IMO.
Never had a problem with availability and just checked Midway and they show 308, 300 and 338 all as available.