Gun Digest annual had a good piece some years back on the many original Nagant '91s that were sold by the NRA pre-WW2 and their sporterization, a near national US obsession in the hard depression years when many country people couldn't afford an American made sporting high-power rifle.
Personally, I'd leave M1891/30s as they are every time and shoot them as historic military curios. If the bore is good, they'll usually shoot surprisingly well if you can get to grips with that terrible trigger! 0.310-312" diameter bullets are pretty well essential in Soviet rifles (Finnish models rebuilt with SAKO barrels are tighter and can perform with 0.308s).
I worked for a dealership that imported refurbished M-N 1891/30s and M1944 carbines from one of the large German outfits, probably Frankonia, who bought them in from Russia. 'Fake' sniper rifles fitted with either the PU side mounted or more expensive PE top-mounted scopes were really good sellers, and I have one of the former. I say 'fake' in that they are ordinary 1891/30s retrofitted rather than original WW2 era sniper rifles. Also around in the UK in large numbers from an earlier period in the 1980s, are a lot of 1950s Polish manufactured M-Ns, carbines, rifles, and sniper rifles. They have a paler finish than the Russian made rifles and may have used a different blander wood, the Russkies being birch. In any event, they were mostly brand new, very cheap and shot well.
I've found handloads with the 123gn Lapua 0.210" dia. FMJ designed for the 7.62X39 over Viht N133, and Sierra 0.312" 174gn MatchKings over N140 or N150 shoot very well indeed. 1891/30s with 174gn SMK loads have won many sniper matches here in Historic Arms competition. The iron sights are a bit too crude to do well in ordinary historic service rifle matches up against 0.303" Enfield Number 4s, P'14s, and Ross M1910 straight-pulls with their aperture rearsights, as well as the 6.5mm M1896 Swedish Mauser.
Laurie,
York, England