One of my pet peeves about the 20rd Tapco mags was that I could never load them with stripper clips successfully. I always envisioned that if I ever had to bug out with a SKS I would take a small number (2-4) of these loaded mags and the rest of the ammo on stripper clips. This would allow one to carry a lot more ammo and reload the mags from the stripper clips as needed. In the event of a sustained battle I wanted the stripper clips to be able to load the mags directly as is possible with the stock SKS mag. Problem was I could never get it to work. I could get the first 3 or 4 rounds in but then it would usually jam.
Well last night I decided to sit down and figure out what the problem was, and it didn't take long. The stock fixed SKS mag has cutouts in the feed lips for the stripper clips to fall into. The Tapco doesn't so the stripper clip doesn't go down far enough and the rounds have about 1/8" to 1/4" of free fall before they hit the mag follower. As soon as the follower starts to offer any real resistance due to its spring being compressed the rounds get forced out of line and jam. I'm no artist with a dremel as you'll soon see but it was a fairly easy task to mimick the cutouts from the stock mag on the Tapco mags and now they work just fine.
Here's what a stock tapco mag looks like next to a stock fixed SKS mag. Notice the difference in the feed lips.
Here's a modified Tapco next to an unmodified one (unloaded).
And a modified Tapco next to an unmodified one (loaded)
I believe this simple mod significantly enhances the capabilities of any SKS using the Tapco aftermarket mags. I don't know if other aftermarket SKS mags need this but as far as I know the Tapcos are the only one's with a track record of being reliable so I don't bother with any other.
In addition, anyone serious about using these mags should also do the bolt mod posted here a while back. It allows you to insert and remove mags without having to hold the bolt back which is imperative for intuitive and ergonomic operation. Performing both of these mods to your SKS goes a long way toward closing the gap between its capabilities and the AK IMHO. I believe it even surpasses the AK in some important areas, not the least of which is to be able to use both mags AND clips. You can carry more ammo on clips due to weight and space savings than you can in AK mags, but now due to this easy mod you can still do the majority of your shooting/fighting with the higher capacity quicker loading mags.