And 400 yds is just the starting point any more.. I would start practicing if I were you.. Perfect practice makes perfect!!I think from what I've read you can expect almost 2 MOA with the Mosin, supposedly the most accurate rifle of it's time which compared to modern day rifles isn't saying much.
I don't care much for 100 year old rifles, I'm sorry they do well at point blank range but I like the option of reaching out and touching someone. If you aren't ready to take a shot at 400 yards it isn't a real sniper rifle.