Had some of these given to me quite awhile back. Just had the opportunity to try them out at the range a few weeks ago. I have heard a few bad reviews of them, but I had no major issues. The one issue I did have was, on all of them, they would not lock the bolt back on last round. Not a huge deal, I actually plan on these being range mags only. Nice to have for shooting on the bench versus a 30 round mag. The price is right too, retail on SG is a 6 pack for under $30. Much cheaper than Magpul 20 rounders. If I was to need a 20 round magazine for something other than bench shooting, I would likely choose something else (like Magpul) but for the limited use I will have for them, I'll go with these and use the savings towards ammo.
