Rob,

What you need to check is not radial movement (up/down/sideways) but axial, fore and aft relative to the cylinder axis, freeplay. It shouldn't exceed .003", preferable just enough to tell there is some, if any. Measure this with feeler gauges in the barrel-cylinder gap with the cylinder pushed forward and then pulled to the rear. The difference between the two measurements is end-shake. There has to be a lot of end-shake to cause mis-fires.

Your photos show completely adequate firing pin protrusion, this isn't the problem.