I haven't been following the current firing issues and potential fixes but I thought I should post an update on mine. I started having misfires again on my DS, so I tore it down and found some pitting on the plate that makes contact with the screw in the button. The problem appears to be arcing between that screw and the plate. I'll bet that was the cause of the melting issues people were having as well.
Previous cleaning with a solvent didn't help this at all so I took the coarse side of a nail file and filed down the uneven corrosion. In the process, I also removed some of the "plating" on the plate. Upon reassembly, my DS is hitting harder than it was when it was new. If you're still having firing issues, try sanding down that plate and removing some of the finish. Now it doesn't matter how I hold the
mod or what finger I use on the button. It fires every time.