Well, this was an “adventure”.  I wanted my specialist units to have a more Grey Knights vibe.  So I searched the interwebs and found a suitable looking helmet.  They were described as Diesel punk Sallet heads for Arcamundi.  I had no idea what that was but assumed it was 28mm scale.  On arrival they were too small.  They are 28mm but I’m guessing the whole Primaris thing…

So I got to measuring them and found that they were about a mm too small.  This worked out at 20%.  I spoke to the maker on etsy and he was kind enough to make and send me the helmets at 120% of the original.

They look great but a little “conservative” for my version of Sanguinary guard the Pretorian guard.  

But they do look great on everyone else like Terminators and my version of Chaplains converted from Inner circle companions…

So I got to looking at helmets and found some Roman style ones.

 On their arrival my initial impression was that they were too small too.  I rechecked the blurb and they are advertised as Primaris.  Comparing them against regular GW helmets they are proportional.  Unfortunately the neck bubble is tiny so they sit far too low.

I’m now experimenting with blobs of milliput in the neck holes and hoping they adhere.

I have since found lots of good stuff on scaling Here - are Primaris 32 or 28 mm