Been messin' with Mosin 91/30's for the last couple of years.
Ignore the frosted bore. It will clean up somewhat after firing some steel jacketed surplus, and will have minimum accuracy consequences; just be sure to clean up after the corrosive surplus priming by starting and finishing the cleaning progress with spraying some Windex down the bore and soaking a bit. It's the muzzle end where bore issues become critical.
Read through
this thread for the odyssey so far. It should showcase the trail of astonishment and woe that accompanies the task of mounting a scope on a Mosin, and finally reveal a simpler, better way to do it.
Nikon? Really? I'm making a $50 NCStar Long Eye Relief scope do enough of the job for now. Some day, when I really lose my mind,
this is on the wish list....
The key advantage of applying the Scout scope system is in how it allows a much simplified way of aiming/zeroing the rifle. Some means of raising the cheekweld with the scope should help, too. Just plod your way through the "Cheap Shooter" thread and methods will be revealed.
Glass/Pillar bedding probably won't have a major impact on accuracy, wrapping the barrel inside the stock channel with 2mm neoprene foam directly under where the barrel bands are may be a better approach. At some point you'll probably throw in the towel and jump for the Archangel stock. I am currently experimenting/evaluating such an installation.
Accuracy is found by applying several simple tricks and handloading has some realistic positive impact on the subject. Prvi-Partizan/PPU 150gr Softpoint ammo is an accuracy step up, and pretty good for hunting, too
Using the simple scope system, original stock, and military spamcan surplus ammo, a basic, bare bones bench rested accuracy of about 2"-3" at 100yd should be a realistic baseline. Improvement starts from there. Don't be too surprised if the Spamcan ammo is hard to beat, it's actually one of the more accurate loads I've tested in my 91/30's.
Also, do not pass go, immediately mount a Limbsaver on that baby. Mosin recoil is surprisingly sharp.
Greg