GP, you have to remove the stock from the gun, there are 3 screws that are adjustable. if you don't have your owners manual, you can download it from the CZ site.
As to the feeding from the mag, here is what I have found with CZ's, first, check the action screws, I just snug mine, some have been tightened like a gorilla. depending on the bedding of the rifle this could cause the action to bind slightly and make feeding and bolt operation a little rough, next I have noticed that some clips feed better than others, I think most of the problem is caused by too much spring tension in the clip which causes a bit of a bind when the bolt is trying to remove a round from the clip, here is what I have done. I polish the feed rails with JB bore paste. I also store the clip loaded full with 5 shells, this has helped relax the spring tension in the clip, now my CZ carbine feeds like a fine custom dangerous game rifle