I used Sgt. Burton's guide found here:
http://www.rhythm.com/~alexko/misc/uscm ... rsion.htmlIt works quite well if you don't have any spare material to sew a new one. My Polish BDU blouse had a fair amount of extra material on the sleeves so I probably could have attempted a more SA collar, but I wasted it trying to make a helmet cover instead...
EDIT: I checked your thread to see if yours has extra cloth on the elbows and it does. Seam rip that stuff off and you *could* make a very nice rounded corner Mandarin collar. It's your call, but the option is there. Of course you are sporting a throat guard so no one is going to see it anyway!!