The term ' Holy Grails ' is a misnomer. Without wishing to throw a damp blanket over this interesting thread, there was only ever one Holy Grail.

The rare pieces that have been discussed on this thread have superstar quality. They are members of small pools of known examples and so far I think it is the fine Anson Star that holds the crown. This one is so rare that it almost trips into the realm of mythology but comes just shy...

The 'Connoisseur ' airguns, the Hermann Historica types, have the highest status in terms of quality and rarity but we are drifting off course, blinded by excellence. We will not find our grail there.

After all the real Holy Grail was just a manky old cup!...

Which is the airgun that fires the imagination?, starts crusades, gets Indiana bumping and scraping under the truck...?

For the late and esteemed Dr Robert Beeman, it was the Lewis and Clarke Girandoni, widely acknowledged as the most important arm in American history. We all know the complex and controversial story surrounding his rifle and whatever the truth, I think the brew ha-ha has added to the mythology.
The Lewis and Clarke Girandoni is similar to other Girandonis, so its claim to the status of Holy Grail relies on its provenance.

My contender for the title is the Walther LP52 that surfaced on egun back-along. I think it ticks most if not all the boxes. It provoked forensic interest and the un-cooperative response from the Walther factory regarding its provenance, helped sustain the element of myth!.
Oddly enough, for James Bond enthusiasts, the LP 53 from the publicity photos that sold for all that money is the Holy Grail...