MG brass

That's actually one of the most common methods of simulating brass casings. You're definitely on the right track.

That's a lot easier than what I used to do 30 years ago: stretch sprue and THEN paint it brass or gold and cut it. A real pain. Go for the wire and snip it. Looks great, it's cheap and simple.

Great idea, must remember that for a future project..

One idea that came to mine is to use insulated wire gagued approximately the size of a spent round, using wire strippers, strip the insulation to scale length of a casing, fill one end with putty or super glue, then paint it a brass color. It migh seem a little time consuming, but it looks a little more realistic having shown one end of the casing open where a slug once was. Anyway good luck and have fun....