kaferhaus is correct
I work at a rifle range in Sonoma County, CA. I have friends who are smiths are I shoot competitively. I own several Mosins. Don't buy a Mosin for accuracy. Most Internet posters describe their groups as 2" smaller and probably would add a similar increase to the size of their manhood. No Mosin can compete with a modern rifle for accuracy and if you try to put money into the Mosin be aware that you'll be able to buy a far more accurate rifle out of the box for the same money.
But, if you are like me and have scores of guns and want to do this as a labor of love here are a few tips that worked for me. #1 be able to do all your own work or have friends who are gun smiths to do the work you cannot do. #2 inspect your potential purchases until you find a near perfect bore. This might mean inspecting 100s of rifles.
I have many 1000s of rounds of pretty decent 7.62x54R surplus I've purchased over the years when it was 3-15 cents / round (Russian Surplus, 7N1, Czech Silvertip). I wanted a good platform to shoot that ammo. My current Mosins were typical Mosins (pie plate accuracy) and not capable of the degree of accuracy I desired. I checked all the Big 5 stores in my area for years looking for one of those Ukranian refinished rifles with an exceptional bore. Eventually I found one that did have a near perfect bore, perhaps it was re barreled or never issued. It's the only surplus rifle I cleaned after purchase that had no copper fouling. At this point I refinished the stock (Amber Shellac), floated the barrel, bent the bold, chromed the bolt, re crowned the barrel with a target crown (old crown was good but I wanted a modern crown), installed a PEM style scope mount and put on a modern scope, did a home made trigger job to get the pull down to about 4 lbs. The instructions for all these operations (except crowning and bolt work) I found on the web. This rifle shoots good surplus ammo consistently about 1.5 to 2.0 MOA with flyers occasionally opening the group to about 2.5 MOA. That's not the best group it ever shoots, that's the average group with surplus ammo. Considering the quality of the ammo that's excellent for a 1939 Soviet Mosin 91/30. Mostly I use it to shoot 3" clays at 300 yards and it can hit those clays about 40-60% of the time if I dope the wind right. I can hit 6" boards at 300 yards 80-90% of the time which is fun when competing against my buddies sub MOA 700s shooting their handloads.
If all these MOA out of the box Mosins exist I've never seen them on the range where I work. I have Remington 700 Varmint and Savage Model 10 Police Models I've done a little work on (trigger, bedding) that can shoot my handloads sub MOA. I'll never get a Mosin to shoot like that. Perhaps with handloads this one Mosin could shoot MOA but why waste time and money loading top of the line ammo for an inferior rifle. My Mosins are fun because they can shoot cheap surplus I don't have to load and if I can hit clays at 300 yards with some consistency and boards consistently that's all I ask.
Here is a good example of the type of false hope you'll find if you rely on the web to find out how accurate a standard Mosin should be:
http://www.theboxotruth.com/docs/edu63.htm
Don't believe that you'll just stick a couple pieces of cork into an old Mosin and start shooting great groups. Unfortunately it just don't work like that.