Took a study break and threw the killstripes on there:
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Here's the template I made and used. I had to cut it up in a few spots to get it to match the curve, but I didn't do it on the drawing. I just cut it up every 3 or 4 stripes.

(click the image for the full-size)
I had some troubles with paint peeling, so to not risk any more I just printed this out on paper, cut it out, taped it on the two outer edges, and coated the underside of the stencil with liquid latex. That helped my stencil stick flat so there was no underspray, and it didn't peel my paint
Give it a shot if you are having that problem. Otherwise, trace it out on electrical tape and it should work nicely. I'm kind of annoyed that I layered it on so thick, since I noticed on the real helmet the killstripes are pretty thin so you can sorta see the green underneath, but I'll probably be the only one complaining 
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