304 sheet hard on one side?

So I'm fabricating some stuff out of 40 mil 304 sheet ('cause that's what I could get from McMaster -- I know now it was a Bad Choice for doing lots of drilling and whatnot).

Thanks to some input here, I'm doing pretty good, but I noticed that the sheet seems to be fairly well annealed on one side, but really hard on the other. Trying to drill 1/16" holes in the stuff, it makes an enormous difference (like, between success and failure with a side of broken drill bit) whether I start drilling on the "good" side or the "bad" side.

Is this common?

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Tim Wescott
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