I tried an M39 on for size once, it’s definitely an improvement in a lot of ways, but I just found the price/benefits ratio didn’t do enough for me. I really liked the rear sight, just the adjustments made sense to me. Ergonomically it’s an improvement I found the stock to be less dainty. All that said.
My best shooting Mosin was a 1920s hex 91/30 that was so clean you could cook out of it. With hand loads I worked myself down to an semi consistent MOA gun, and I had so many other Mosins that gave me various perks. Ultimately I sold the M39 because it was just too much to have wrapped up in what was ultimately just another Mosin.
To me anyways, maybe others, it’s a utilitarian action by design, and so the idea of working it into this fancy rifle the Finns made, is great, but it’s like having the sharpest butter knife in the drawer. Other than the looks and feel of it, there’s a lot of other variants, even Finnish that you can attain cheaper, that have cooler history and are tooled just as nicely.
Just my two cents.
I realize it's your personal opinion that Mosins are "utilitarian" but I disagree with that opinion.
At the time of their introduction, they were cutting-edge tech and influenced a lot of firearms designs around the world.
The bolt is complex when compared to most others but absolutely functional and reliable when it's properly maintained. The actions are strong, well-designed and smooth as glass.
They were designed to last for decades of hard use, then able to be torn down, have worn/broken components replaced/swapped/salvaged, and put back into reliable service for more decades.
Utilitarian instruments aren't designed for such use for the most part.
I have a Mosin M91 with an 1898 date on the chamber. It's been through a couple of refurbs but still maintains its original design features.
It still shoots very well with just about any milsurp or commercial ammo. It still does everything it was designed to do and does it with reliable consistency every time I shoot it.
The Mosins we normally see are in military garb. They appear to be "utilitarian" but are IMHO anything but
I've seen several Mosin sporting rifles that were purpose-built as such, and they wouldn't look the least bit out of place with any other fine sporter of the period.
I can tell you appreciate and like Mosins, but I get the idea you see them as "cheap" shooting alternatives, rather than the fine pieces of workmanship they are.
Mosin actions are usually smooth as oiled glass, which can't be said about other bolt action rifles of the period.