I have a friend who owns a .223 HK (clone) SBR and I was shocked by the dimensions of his fired brass. I was unable to get any of it to enter my gages, with at least 1" of case protruding from the rear of the gage when the case gets stuck hard and needs to be knocked out with a punch.

Headspace is long and the chamber is huge radially. Of course each case has the familiar striations associated with HK's fluted chambers, but that doesn't account for the incredibly large dimensions. I almost stuck  several cases in my resizing die even though I was using Imperial sizing die wax. I have never stuck a case in any die in over 35 years of reloading.

Is this common or should he have his rifle inspected for excessive headspace? I'll try to post measurements of the enlarged case body.

It sounds normal - it's a delayed blowback action.  The case is extracting before pressure drops as low as it does on an AR.

I've reloaded thousands fired from a V53 though I never gauged a fired case.  

Resize it, then inspect again.  It should come right back to spec.