Oh lordie. Note that drilling in metal is done in stages -- it's totally unlike woodwork in this regard.
First you drill a pilot hole, like 1/8". Go as slow as the drill will allow -- as mentioned, you should see shavings or chips, at least. Ideally you'd get two long shavings, one from each flute of the drill. If you aren't getting metal coming up, slow down. Also use cutting oil, tapping oil, something. I like Relton's Rapid-Tap, but even the Ace thread cutting oil is better than nothin'.
Then, you go a few sizes bigger than your pilot hole, then a larger bit, etc, to the final size of the hole (7/16" or whatever.) You do NOT, no way no how, start with the 7/16" bit, or you will be buying them in bulk.
You'll find the first one, the pilot hole, will take forever, and after that they go pretty quick.
You may know all this, and if I'm preaching to the choir I apologize. If you didn't know, though, it would 'splain why you had such a tough time...
-- A