In a nut shell, light ball is 147 grain give or take, heavy ball is around 180 grain something. Steel core has a little plug of steel in it. Looks like a roll pin. When the bullet disintegrates say in a dirt bank, you can actually recover the little roll pin steel core bit. Much of this ammo has painted tips(but not all), i.e., yellow, to distinguish it from other types. IIRC, it was because the troops might use one kind in their bolt rifles and another kind in their machine guns, thus the painted tips.
I like the heavier stuff, works better at long ranges but YMMV. Try both and see what your buddies rifle likes.
Also make sure he shoot his M44 with the
bayonet extended. Otherwise the groups will be a bit off, especially at the longer ranges.
That's the way it was designed. It's not a biggie at real close range, say 100M or so. Again YMMV, so check it out when you shoot it for accuracy.
Here is a linky to to check out the various ammo types:
http://7.62x54r.net/MosinID/MosinAmmo.htm