Got a HK91. Been reloading for this gun for years.
Fluted chamber causes flutes in brass. Since the brass is extracted and ejected so fast,it dings off of everything. My gun throws brass 20-30'.
I use a heavy amount of lube,run the brass into the die slowly,partially lower the ram,turn the brass 90-180deg and run it back inside the die. I full length size it also.
Some of my brass has been reloaded 6-8 times. All brass for this gun is heavily mixed using both civilian and military.
These guns will absolutely eat everything. --- SAWMAN :-)