I'm very new to these coils, so bear with me. I have only built one coil on a regulated device which is more forgiving as you can just throw power at the coils until they work. I have no experience with claptons on a mech but:
The core wire is the key in targeting the desired resistance. The wrapped wire adds mass and surface area, and to a large degree will not affect the final resistance. On a mech your voltage is fixed, so a low resistance is prerequisite.
Start out with 7 wraps of 24g at 2.5mm wrapped with 32G which should come out to out to about 0.3 ohms producing about 60W (to begin with, then rapidly dropping). If this doesn't do it, try the same with 7 wraps of 22G 0.2 ohms (88 watts). You can also use a twisted or parallel core to produce a low resistance.
Once you have built the coil check it on an ohm meter before installing it on your mech. You need to gently pulse the coils gently, squeeze and rake them gently to iron out any hot spots till it glows evenly.
Please, make sure you are up to speed on battery safety. Any questions on this, feel free to ask.