However, I have found a set of mics that I think do very well as "reversely engineered" SM-57's and SM-58's. They are made/imported by Orange County Speaker (
www.speakerrepair.com) - the thing that convinced me to try them is the fact that the mics are designed to pretty much exactly emulate the frequency response of the 57/58 capsules (with pretty much exactly the exterior construction as well). This includes the cardioid pattern and off-axis rejection.
The proof is always in the pudding, and I've now been using several of each type for over a year - directly alongside SM-57's and SM-58's - and they've performed flawlessly. In fact, the SM-57 clone is slightly "better" sounding in my opinion; the SM-58 clone is actually a slight bit more linear in frequency response, so the vocal tone is more clear but less colored than the actual SM-58. I like the SM-58's frequency "hump" so I'd probably prefer it to this company's mic slightly; however, for $39 I can almost buy three of these to one Shure 57. In the end I decided to populate the studio (garage) with the Audix OM series for recording, but I use the SM-58 clones for live performance. They work great.
That's my .02 worth. I don't work for Orange County Speaker...don't get anything from them (mandatory disclaimer

). I will say their customer service is fantastic...once got an instrument cable from them that was slightly frayed in two spots (cloth covered cable). They sent me a new one, no questions asked, and let me keep the other one (which worked just fine) as well. They give you a "no questions asked" guarantee on the microphones should you not think they sound as good, or better, than the SM-57 or SM-58.
Jay