There is NOT 17,000,000, Mosins Nagants that survived two World Wars, a Revolution and myrids of "give aways" in military aid after WWII, by the Soviet Union.
Still , only Accurate rifles are interesting.
My Sako built MosinNagant M-39, with open sites, will put 5 in a 3 inch circle at 400 yards.
Accuracy problems can be much more a problem than to solve with adding a scope. Proper Riflemanship , good tight bedding/shimming, a smoothed trigger engaugemnt and often recrowning, via shortening the actual barrel or counter boreing to remake the crown, restore accuracy and keep th ebarrel length, but that usually an arsenal job.
The third point to accurate shooting , given a good man with proper skills, a good rifle with all mechanials working is that you need quality, consistant ammo.
Soviet block silver tips are 150 or so grained 'light ball' made for the sights and shoulder of a Mosin , the yellow tip indicates 'Heavy ball', used in overhead fire by machinegines. When the heavy ball was dropped, the silver tip was no longer done and ball without color coding is 150 or so grain, inteneded for the Mosin.
being an avid and well practised shooter, I can say with personal experiance that most heavily graind Commercial "hunting ammo' will not shoot to point of impact with the sights on my Mosins. You'll have to shoot, see, adjust and use that same brand and weight of ammo. practise shooting the very ammo you plan to hunt, snipe, plink with.
I use cases of Czeck Light ball to great effect because the cionsistancy and practise has me knowing that rifle soooo very well.I just know where to hold, and was doing that with my .22 when I was a kid, same same.
Use the right ammo, and watch your groups shrink.