I have not posted in years, but thought I would chime in. I just got back from Eastern Europe, and made my Ruger dealer very happy, as I have been replacing my armory that I could not have where I was, except those utilized for work. At any rate, I also just purchases my 4th Ruger Gunsite, synthetic stock stainless model.
AICS metal mags are well made, which is why they aren’t exactly cheap. There are two different versions of polymer mags now from Ruger, ranging in capacities of 3 rounds, 5 and 10. The polymer mags from Ruger are a bit more compact than the metal ones, and the polymers also allow for top loading while the magazine is still chambered, whereas the metal variety must be removed and cannot be topped off while in the magwell. Though they all interchange, I am using polymer mags with the synthetic stock, and use metal mags with the laminate rifles, but for no particular reason.
Since you’re new to the GSR, I will give my $.02. Being used, I would check the action bolt, make sure that it is torqued to specs (different for polymer or laminate rifles). If you ever wish to really get the best of accuracy, Federal Gold Medal Match, has worked great in all of mine, though yours may like a different brand, usually you will find a match grade ammo that shoots well, (the twist ratio seems to prefer weights of 168 grain and heavier) as mine have all been MOA, with a couple of them being 3/4 MOA rifles when I did my part. All of mine have worn leather from Andy’s Leather, and his Rhodesian sling works great with most carry styles, be it American, European or African carry style of slinging it. I know a lot of people do not use slings, but if you’re shooting offhand, with good technique it will really help, if you are so inclined. This latest one of mine, was going to be a basis for a custom, chambered in 338 Federal, but I have just decided to get another, instead of touching this one.
Hope this helps! Happy shooting!