Is there anyone here who have experience with the caliber 45-120? I have heard that it�s very difficult to get this caliber to shot good. Also they said that the cases broke becourse they are very thin.

Karl-Erik- Brent gave you the straight skinny here. And he knows exactly what he's talking about as he has a number of years being a dedicated rifle crank with the large capacity
BPC rifles.
If you haven't already bought a .45-120 I'd avoid it like the plague,under any circumstances but particularly if you're reletively new to this type of shooting and loading, for whatever reason the Italians are fond of chambering thier Sharps repros in this caliber, likely it's the magnumitus thing where guys want the biggest baddest unit on the block, the only thing worse than a .45-120 I can think of is the .50-140 in either case they will be exceedingly difficult
to work up accurate loads that can be dealt with at all in the fouling department and they both will pound the snot out of you. Back in the day before Quigly Down Under came out, you could order up a Shiloh Sharps for less than $700 from
my friend Dick Greensides (Pecatonica Long Rifle Supply) lots of the guys, particularly younger
folks wanted these monster chamberings and couldn't be dissuaded no matter what you told them invariably once they actually recieved thier rifles they suddenly became uncharacteristically silent about their new rifles, however you would see most of them for sale on the club bulletin board there was somewhat of a glut of these so they went for bargain prices so some of the more experienced shooters would buy them and set back the barrel
or re-barrel in a more intelligent and reasonable chambering, I wish i would have bought a Shiloh back then, at any rate if you are newbie do yourself a favor and start out with a .45-70 and save yourself some serious money on dies moulds etc and you'll have a lot easier time getting the loads worked out, or if you're somewhat recoil shy get a .40-65 and get much the same benefits. If the .45-120 you're looking at is the IAB or IAR avoid it like the plague also, I had the infortunate experience of owning one and it was an absolute POS. I think the least expensive quality BPCR's are the Pedersoli Sharps and the Uberti High Wall, and I'd just go with a basic one as the Italians versions of sights in my experience are dreadful, and you end up paying a small fortune for thier POS sites, a German silver nose cap and some checkering
for that kind of money you can put 1st class useable sighting on your rifle.
Regards fredj

Have to agree with the two other posters,I have two of the 45-120's,both on Rolling blocks,and they required some modifications to the hammer,I have not had any trouble working up loads that work,but recoil can be a problem with the higher loadings,as far as I can tell the Italian rpos are junk jave talked to several at single shot express and they all say stay away from them.
For pure enjoyment,try a 40-65,40-82,45-90,45-110 they don't burn as much powder.