Thanks for re-confirming the caliber.

I'm a very old and very big fan of Mauser's. I still consider the M98 as the best action ever created. And I'm delighted that the creativity, ingenuity and mindset of some gun lovers and gunsmiths are refurbishing and modernizing the old rifles and receivers.

Now the plot thickens. Even in the face of the proof marks in the photos there are new questions.

1. Caliber 6.5 x 55 mm. That's Swedish King Gustaf.
2. Someone observed that the "crown" stamping looked Swedish.

Some Swedish Mauser's were made in Sweden and some in Germany and some privately. The practice of Swedes was to rank the guns by stamping categories and the crown meant approval while an X meant disapproval.

https://en.wikipedia.org/wiki/Swedish_Mauser

http://www.gotavapen.se/gota/mats/marks_mauser_rifle.htm

Here also are photos of Mauser proof marks. The Crown shows in some.

https://www.google.com/search?q=swedish+mauser+proof+marks&rlz=1T4GGHP_enUS512US512&tbm=isch&imgil=EAJqWs6ptfAAAM%253A%253Bn6tlX0XrE-Gt_M%253Bhttps%25253A%25252F%25252Fwww.msgo.com%25252Fthreads%25252Fswedish-mauser-markings.31496%25252F&source=iu&pf=m&fir=EAJqWs6ptfAAAM%253A%252Cn6tlX0XrE-Gt_M%252C_&biw=1024&bih=395&ved=0CC8QyjdqFQoTCJXfo6KB_cYCFULVHgodHsQH7Q&ei=5ge3VZXUDsKqe56In-gO&usg=__ltN21BGBBbzPzm50BS5vIUCWVGw%3D#imgrc=EAJqWs6ptfAAAM%3A&usg=__ltN21BGBBbzPzm50BS5vIUCWVGw%3D

So? The ID is not yet 100% confirmed.

On a personal note I would have liked to have my Swedish King Gustaf customized and modernized but it was from an estate collection and in more than very good condition with all matching numbers. It also came with various soldier field accessories such as bayonette, cleaning kit, ammo packs, lube kit. I couldn't break it up and destroy it's original collector values as an authentic.