Nothing done to it, but it's an actual real one, not a "repro"; scope number matches that on the side of the receiver. Very nice bore... so although I am not surprised it shoots well, I am surprised to what degree it shoots well!
I have a similar rifle to the one you have. The matching scope was replaced somewhere along the line before I got it. The replacement scope has been refurbed but is original from the same period. The stock on my rifle and the scope bracket are beat to hell, looking like they've been there, done that. The refurb PU scope looks odd. The barrel has the same number stamped on the left side as is on the scope bracket. The bore on my rifle shows no wear and is bright and shiny.
Like your rifle, this one shoots most surplus ammo very well. Can't say the same for the MOLOT clone. The PE scoped rifle is original but FTRed it also shoots most surplus well.
My other Mosins I have, Russian 91s, 91/30s, couple of Finns and a Hungarian marked rifle are fussy. The M91 Finn and the M29 Finn aren't fussy about what they shoot but they still aren't as accurate as the two original snipers.
Like you, I haven't made any changes to them.
All of them shoot much better with the two methods I mentioned. I seldom go through the time and effort to follow the second method.
I had one M91 that was converted in Europe to a hunting rifle a long time ago. It had folding rear sight leaves, marked out to 400. Not sure if was Arshins or meters. The date on the barrel was 1910. There was a Czarist crest on the top flat of the receiver. This rifle was fussy. It also had a 1-12.5 twist rate and wouldn't shoot anything over 154 grain bullets with a flat base well.
Lovely rifle, tasteful engraving on the receiver and first third of the barrel, to the rear sight. Very fine checkering on a well figured Walnut stock, with what appeared to be a bone or ivory fore end tip and butt plate. There were four holes drilled on the underside of the butt with a hinged brass cover, to hold four cartridges.
The comb on the stock was a bit higher than on military rifles. No raised cheek plate. The trigger guard and Magwell were also tastefully engraved, only along the bottom edges on each side.
It was chambered for the 7.62x54r.
I needed a new 200amp service panel/mast and 6/0AWG wire, along with a bunch of breakers and several spools of NMD14/2, 14/3, NMD 10/3.
I sold that lovely rifle, with it's original hinged, leather, fitted case, dies and cleaning accessories, built specifically for the rifle, to a gentleman by the name of Mickey Moody, from Kelowna, for more than enough to pay for the electrical supplies I needed. Mickey was a real gentleman, rest his soul. Well respected on the Gun Show circuits and a knowledgeable gunsmith in his own right.
I miss Mickey and was pleased to see that he kept that rifle for close to 20 years, before it went for sale from his estate. I should have bought it back, but my eyes were changing and not up to those express style rear sight leaves with the very shallow V filed into them.