Further comparisons on rivet head formation: custom flat vs dished nose-piece

Some flat nose-pieces were formed from a cheap rivet gun's nose pieces by grinding an polishing. The results observed are consistent with the previous tests. The open question is whether the region of extended contact a byproduct of the unpredictable nature of the small-but-quite-not-zero gap formed, or due to a machining error when creating the heads. I think it the former, as everything self-aligns with considerable force when setting the rivet - and this assymmetry has already been observed.

The only remaining issue with whether there is any engineering impact due to the slight dishing of the rivet head underside when a dished nose-piece is used. This is more pronounced with the 4mm rivets. As of now only some empennage and wing internal structure have been rivetted: no skins. I will query this with TAF.