Friend and myself played with several of these for a number of years, actually got some very decent iron-sight shooting out of a couple.
His trick was to 'take care of' that long, slender fore-end. You know the one: it wags like a pup's tail ahead of the main stock of the rifle. Likely they were fine when they were made; the wood was made that way to protect the shooter's hands and to provide a relatively light control on the muzzle. The problem is that Time is NOT on our side and 70 or 90 or 100 years is enough for even the best-cured wood to warp..... and nearly all MNs were built during wartime, anyway.
So we glassbedded the frame solid, so as to keep the rifle and the stock in the same place at the same time (we had discovered that 'more or less' just doesn't cut it with the MN). The slender fore-end we took care of with a 9-inch length of 1/4-inch steel rod which was buried in the woodwork (after routing out the channel very carefully) for about 4 inches at the belly of the stock, the remainder under that floppy fore-end so as to stiffen it. When everything was good and solid, we installed a half-inch pressure point right at the front of the fore-end. Rifle shot very nicely out to 400.
My friend then determined that he wanted it better yet, so he glassed in the cleaning-rod (!) and shot it like that.
For the next 4 years, every trip to the range the first 3 rounds were out of the old MN, shooting at a 4x6 piece of tarpaper at 325 yards chained, and that was Summer or Winter, 90 above or 30 below. They were ALL on it.
Gavin Tait regarded the test a success and the $169 expended on the rifle (with all equipment) as money well invested. I just learned a lot.
BTW, we were shooting WITHOUT the bayonet attached. The Russians issued no scabbards for their bayonets; they were kept fixed at all times. It looked great in a parade, but I think that part of this would have been to ensure sufficient pressure on the relatively-flimsy stock at the muzzle.
Hope this helps.