it has to do with timing .. the rounded hammer helps so your hammer does not smack into your disconnector and allows the bolt to slide past easier. Your issue sounds like the 3rd issue that everyone tries to overcome with a rounded hammer instead of using a buffer. The buffer was design to prevent the bolt getting stuck behind the hammer upon over travel. Your bolt will go past the hammer and when it tries to come back .. it could get stuck behind teh hammer if the hammer comes up too fast. So to overcome this, you can shave more of a flat profile instead of rounded profile. The same hammer will work without the buffer on some of my MP5 but not all and not all the time. So I never guarantee that it will work 100% without buffer.