Got caught up in all the Mosin madness a while back and picked one up for $99. I took it shooting and found that it grouped like a shotgun, (Nearly 10" groups at 100 yds.). I took it home and did a more thorough cleaning in good light and found that the stock was cracked under the receiver. you can also see that the rear area of the stock where the tang sits is uneven and makes for a poor contact area to bed the action. This may have contributed to the cracking in the first place.
I took this as an opportunity to try some stock repair techniques and see what kind of accuracy I can wring out of the rifle.
Here I put some epoxy in the crack and then used some wood clamps to clamp the stock together, then drilled the stock and put ins some brass screws to reenforce the stock and prevent the crack from traveling under recoil.
After cutting the screws off close to the stock, I used a fine file to take them flush to the wood.
Next I decided to try to take care of the bedding surfaces for the action and the recoil lug area to not only make a secure bed for the action, but to also help make a solid fit that would prevent future cracking. I used JB Weld as my bedding compound and paste wax as my release agent when bedding the action.
As long as I had it apart I figured I'd check the barrel channel to see if there were any tight spots for the barrel that could put uneven pressure on the barrel, affecting harmonics and shifts as the barrel would heat up. I slid a piece of paper under the barrel to identify tight areas where the paper would drag, and marked these areas with a pencil. Then I used a deep well socket and some sand paper to locate and smooth out the tight spots. I did this through the barrel channel up to the area about two inches forward of the flare in the barrel near the action, until the paper would travel smoothly down the barrel channel.
Some rifles will do ok if the barrel is floated for the full length of the barrel channel, while other like to have some upward pressure in the last couple inches of the barrel channel. Thin cork was used by the Finns when they accurized Mosins and placed in the end of the barrel channel to apply this pressure. The Finns also used metal shims in the tang area and lug area as well as under the trigger guard to provide a bedding surface for the action.