The thing about Mosins is that the quality of the guns, snipers included, was all over the fucking map. Some were very good, some weren't, some were god-awful.
That's the real shame with the gun, compared to the bolt guns of other armies.
Look at the No4mkIT, the Enfield variant sniper. It was purpose built, accurized, and had to past rigorous muster before being issued. Thus, it was VERY likely that your issued No4 sniper was VERY accurate, and consistently so.
The Mosins were, in a manner of speaking, slapped together as sniping platforms and their performance shows it. Some are MOA capable, some aren't pie-plate accurate.
That's just a byproduct of the way they were built and the standards the Russians kept. They were plenty capable of making superb rifles, but they didn't always do so.