there are a few different ways, first is to buy the reproduction units and drill and tap the receiver, next would be to install a scount mount that replaces the rear leaf site and use a long eye relief scope. the latter is the most popular due to price and the fact that you don't permanently destroy the guns historical value. if you would like some links for these types of products just let me know and also tell us what type of ranges you'd be interested in shooting and also what model of Mosin we are discussing.
i heard if you remove the pins in the rear sight base and remove the whole sight base that there is a rail under it you can use for scope mounting , but i heard you have to use some tall sight rings . wait for someone to agree before doing it tho , i hear lots of stuff .
It wasn't alot of cash, I think I have around $260 in it without the scope, scope was $80. But, I did have a buddy who is a gunsmith, drill and tap the receiver, install the bent bolt and cut, thread and re-crown the muzzle all for $50 which is reflected in the total price.
Yes! Go to the S&K scope mount site...get the mount from them. It goes where the rear sight is...easy to remove rear sight and install yourself. Use a pistol scope 2x... or better if you need it. Works on 91/30-M44 or M38. The M38 scoped makes a great deer rifle.