I would not encourage anyone to use a .204 for deer. And as a Hunter Trapper educator we strongly tell our students to NEVER take a head shot. Not under any circumstances. Why not? Because we've seen on walks after season with the Game Commission a couple deer a year that did not die from a head shot! These deer starved to death because the slightly misaimed bullet hit the skull and was diverted downward taking off the lower jaw. The poor animals suffered a horrible death either by starvation or being too weak to escape coyotes or bear.
Please don't ever take a head shot.