You're comparing a target shot with a scope to issue iron targets? My target was shot prone, issue iron sights with the issue Mosin sling. No lead sled, sandbag or whatever. Yours?
I wasn't actually comparing your target, otherwise I would have quoted it. Yours seems good. The one I quoted with the "sks could never do this" was nothing special.
The last pic I put up was a Russian SKS, completely factory stock. All groups were fired from a tripod, and a rear sandbag. I don't have a lead sled.
When you shoot groups, the whole point is what the rifle is capable of. What the accuracy
potential of a rifle is. If you take a modern bolt action .308 and use it with iron sights, you won't get as good a group as if you put a scope on it. Using a scope will let you know the true potential of a rifle is. I've put scopes on Lever rifles I never intended to use while scoped, just to work up loads. Even if you can't shoot MOA with iron sights with a lever gun, the rifle is often capable of it, which is why using a scope to work up loads makes lots of sense. Same if you want to see the true accuracy potential of an SKS barrel...
The failing of the SKS in regards to accuracy is primarily it's poor sights, secondly would be it's trigger. And some people find the stock too short. If you improve the sights, and learn to use the trigger, you are well on the way to good accuracy. Most people don't do this, and therefore the SKS is considered a Barn Door MOA rifle.
It's good to establish what your rifle is capable of. MostSKS rifles are more capable than their shooters, but most people just live with whatever accuracy their poor sights give them and have fun. Nothing wrong with that, BUT...... There are certainly some things that make it EASIER for a shooter, and good sights and trigger are possibly the most important.
I recently acquired an SKS with a HiCal mag adapter and a High Tech aperture sight. If I do my part, I can hit a 6" gong at 100m 10/10 offhand, using the issue sling. I think that's more than accurate enough for a "plinker" rifle that the OP is looking for, which is why I suggested the sight upgrade. I'm sure your Mosin is capable of better accuracy