From my hammock camping forum--one Ralph mentioned a hole punch available at harborfreight.com. I could not find the one he mentioned-but, their hand punch is made to put holes in thin steel, aluminum and brass. It seems to have a wide gap. And, it has punches for circular holes of the following diameters: 2, 3, 4, 4.5, 5.5, 6, and 7 millimeters. It costs $20 (plus shipping charges) but would allow for versatile experiments with different hole sizes.
R Blake, Flagstaff, AZ