I want to put in a second downspout at the end of a gutter that can get overloaded in torrential rains. I have 5", half-round, galvanized steel gutters that are fairly heavy gauge. Since it's half-round, there is no flat bottom to drill into. I was thinking of using a bi-metal hole saw with a pilot bit, but wanted to hear if anyone had a better idea for putting in a hole for the round downspout. Thanks.