Mosins are fickle. What amm one loves, the next hates.
The most consistanly accurate for me have been the 148-gr Czech silvertip and the 180-gr Hungarian LEAD CORE heavy ball. the Hungarian steel core heavy ball has not been as consistant.
Some of my Mosins are real tack drivers with Albanian ammo, most shoot good with the Chinese ammo I have, but not as good as the Czech or Hungarian ammo.
I hear tell the Polish ammo is good, but it dried up before I could get any, and people are asking crazy prices for it now.
As for the bayonet, it usually won't affect group size, but sometimes will shif tthe point of impact. But ti's a harmonics issue and each rifle is different. With some gun/ammo combinations, it makes no difference, with others it moves the point of impact a couple feet at 100 meters.
It all depends on what your rifle likes.