beginner, yes, they are free to rotate but as they rotate about the axis of the pin they always strike the case rim, and the center is where your firing pin protrusion is measured. I have examined many of the fired cases and they are all well hit; the purpose of the slight \'chisel-edge\' merely allows the firing pin to penetrate a bit with the slightly weaker main spring, it still speads over the whole diameter of the pin. This is only a slight angle, maybe only 2º to 3º per side at the most. Try it first without the angle, I only had a few soft hits with the flat ends when I first started using the .038 dia. wire so I decided to reduce the area of the initial firing pin impact....and have never had a \'soft\' strike since. These firing pins are available from Reid or MSC and are just mold knockouts; they can be purchased either soft or hardened, I buy about 30 or 40 at a time.
Maybe you should stick to the plans as written for now, always time to experiment later
Dick C. (gatguy)