I own about four flavors of Mosins now M44, 91/30, M91 and M38. And I would offer this wisdom.
1)If you get a carbine (M38, M44 etc) then recoil is cut in half when your standing up -vs- sitting at the bench. I can shoot standing up all day but 50 rounds at bench with a carbine is enough for me. Sitting bruises my shoulder black and blue but standing does not. Why? Because standing up your entire body soaks up recoil -vs- sitting your shoulder alone gets the brunt of it.
2)Sometimes mosins have a buildup of laquer inside the chamber fromt he cheap steel laquer coated cases. you can clean this out with a wire brush and cleaning rod attached to an electric drill. Use some kind of solvent when you do this. Some say to wrap some fine steel wool around brush before you do this but I would not recommend that as this will actually start taking away metal IMHO.
3)Many of these rifles were sighted with bayonet fixed (or extended). What this means is that since most ranges will not let you affix bayo, you will need to re-sight your iron sights windage setting. A small hammer and flat pin punch come in handy here and remember that only small amount of taps will move it usually. You will also need lots of ammo to test this out and start this on a short range 25-50 yards first then move on to 100yards or longer.
Most of all, be safe and always check to make shure gun is empty when working on sights. Take bolt out every time to be sure. You can also buy a laser sight at wallyword for $30 that will help you check alignment out to 50 yards before you even go to range.
These rifles are an absolute bargain in this day and age although there are millions of them, they won't always be this cheap so I encourgage everyone to get one, even if you don't shoot it. It makes a nice wall piece. Keep it for prosperity etc.
The 54R is comparable to .30/06.