first time shooting my SAR-1

Finally got a chance to get out to the range and shoot my SAR-1 AK. Also the first time I have ever shot an AK, and now I see why they have such a following!!! This gun is awesome, I could have sat there and shot it all day. The only problem I had was with one of my 30rd mags, it would not feed. Once I compared it to the other 4 I realized it has a different follower than all the others. Are followers pretty cheap to buy? Would that be the cause? Mu wife to my camera to the beach so the best I can describe is that the ones that worked have a raised side on the top of the follower kind of shaped like a cartridge. The one that did not work had a raised side on top of the follower that went the whole lenghth of the follower and was more boxed.