Copper isn't going to fragment, and if you make it barnes x type, it *might* be decent. Actually it would be should better than any other controlled expansion round .224 bullet. If you can imagine 4 long strings of copper connected to a long shank, of course, how long the strings of copper would be dependent on velocity. Or you could just have a 75 grain hornady. Or a 100 grain BH. I don't see what is so bad about the trajectory. It in NATO pressure , it was hypothesized that it could go up to 2600 fps with no problems. Even if it was only 2500 fps, it is starting out faster than most 7.62x39, and with a bc in excess of .500, it is going to shoot considerably flatter shooting than any loading of 7.62x39.
It was made to be a very lethal load for short barreled operators. Ballistic testing has shown to be promising. Lead fragments, copper is tough. 5.56 lethality relies on tiny fragments impacting the inside of a tightly streched temporary cavity creating a wound far in excess of a controlled expansion round.
Nothing against copper as a bullet material, just not in this sort of application. And if you want to experiment, just get ahold of an experienced reloader and your local machine shop, cnc would definately be better due to tolerance and higher volume for testing. Everyone would be overjoyed with the testing of soemthing like that.
whisper