0.5Ω is pretty low for a KF atty. If you consider surface area, at only 4 wraps... that's pretty minimal for 0.5Ω. The more surface area, the more juice on that surface area to vaporize. Kayfuns tend to run better with 7-11 coils, so you'd be better off with 7-8 wraps:
28 = 1.0~1.2Ω.
27 = 0.8~0.9Ω.
26 = 0.7~0.8Ω.
My personal preference is 27 ga. at 9 wraps for 1.1Ω or 26 ga. at 10 wraps for 1.0Ω.
Click on my first sig line hyperlink... you can run coil models, and in the advanced mode, review surface area information. Get the maximum surface area for a given target resistance... within reason and physical confines of the atty of course.