The metal mags are hit and miss. I have 3 sks and 4 metal mags and find a bit of variation between them, despite the fact that they are the same maker, and came together. The top lips and the follower angle seem slightly different from mag to mag. The fit is off on one as well, as is the rear tab on another (easily fixed with a little ingenuity). The tapco 20 rounders fit all guns very snug, but without mods, and fed perfectly with no stovepipes. Bolt hold open works on all of them, but I do find reloading them with stripper clips while in the gun is a bit of a pain on one. The guide seems slightly further back then the magazine, an issue that didn't exist with the metal mags and that particular rifle. Over all, I think the tapco is the way to go, having much tighter tolerances and consistancy.