I’ve seen different types of P38s, and some were better quality (and probably different steel) than others. I’ve always had the best firesteel experience using hacksaw blades. You can use a vise (or pliers) to bend them back and forth until they snap to the length you want. Then use some sandpaper or something to shape it. Another tip, instead of holding the firesteel still and moving the striker to strike it, you get better results if you get in close to your tinder, and instead hold the striker steady and move the firesteel away from the tinder (scraping it on the striker) instead. You can get closer to the tinder instead of doing it the other way, and the less distance to the tinder, the hotter the spark will be.

I like big fat firesteels. They last longer, and make larger, hotter sparks. Here’s where you can get 4” x ½” thick ones: http://www.epcamps.com/4in_Flint.html

Here’s a good article on flint and steel, but you may find it useful as well: Tips for Fast Fires with Flint & Steel, by J. Gottfred