The chamber flutes are supposed to allow powder gas to get between the expanded case and the chamber to allow easier extraction.
HK used the same principal in the CETME based HK91 rifle and P7 pistol.
I have never heard of any with holes drilled clear through the chamber.
That would not work, as the fired case would, if not blow out, expand into the holes and be firmly locked in place.
BTW: The Automag II was designed to work with Winchester Super-X .22 Mag 40 grain ammo.
It is doubtful you will get them to work well, or at all, with anything else.
rc