I am assuming that 7.7 marked on the bottom of the barrel of original Mauser commercial sporter indicates caliber 8X57J. Is this correct?

I'm certain 7.9 or 7.92 is 8mm Mauser

Ok, let us not forget that there are, or were, two different versions of what we now call the 8x57; (not a Mauser cartridge).
One was the 8x57I (J) up to WW1 or so, which has a .318 groove and one 8x57IS (JS), .323 groove.
The marking on your barrel only indicates the bore diameter, so 7.7 is .303; it could be and probably is what you think. Might also be the 8.15x46r. Or some other cartridge with a .303 bore.
The 7.9 which is customarily found on military barrels, referred to above, has the bore diameter, .311.
Cartridge nomenclatures are never uniform even in the Metric system and is not very precise to use for us used to measuring barrels in thousandths of inches unless carried past two decimal places.
There might be more clues on your barrel, or maybe not. Those early rifle makers assumed the owners knew what caliber they had. Might need a chamber cast if there are no other marks.

It isn't my rifle. It's listed for sale: https://www.gunbroker.com/item/796577489

This old post may help shed some light on the 7.7 marking too.


http://ww2f.com/threads/rare-g...ehr-variation.47336/

All of my Wehrmannsgewehrs are marked 7.8, which means nothing.
I note on the barrel, the 222.5 marking; this is usually the twist. 8.75 inches?
Have him send you a picture of the bolt face and extractor; that will tell a lot about the caliber.

We have here conflicting markings. The 222.5 is a gauge marking, denoting a 7mm bore, and next to it the 7.0 marking seeming to support this. But on the side of the barrel we have the 7.7 marking. A rebore seems likely.

I love these type of listings. It's like the Dating Game.

Bachelor number one. are you a 7x57.
"Oh I never tried that."

Bachelor number one: are you an 8x57.
"now your getting kinky"

Bachelor number one: Did you ever do a chamber casing.
"well I was cast in a movie once."

At least he took pictures.

There's no money in figure out what it isn't??

dovetail through the front ring.
Claw mounts No scope rings.
Only a surface crack

To add to the mystery, there is another explanation for the barrel marking of 222.5, which would translate to a twist rate of roughly 8.5 inches. This would be correct for a 7x57 or 7X64. The magazine arrangement appears to be normal for a rimless cartridge, meaning that it would not accommodate a rimmed cartridge like the 8.15X46R.

A rebore would require another proof test, and there is no indication that the rifle was proofed more than once.

OK, here's what Jon Speed has to say:

Bill,

Ok, we have a Intermediate system rifle in 7X57. Non Oberndorf Scope bases. The under barrel data shows Bore gauge number 222,5 = 7mm . What's odd for me is the designation 7,7 normally indicates a .303.

I see a crack on left side of forend but at the lip where it meets at Junction of the front of rear sight base inletting inside stock I see crack extend to inside of stock= all the way through at that zone but maybe Not through main body of forend.

Some fool flattend the pear shape bolt handle for scope clearance.

That's all I can offer on this example, In my master SN list are 3 other 7X57 rifle as well as a Rigby 7X57 all within same SN ranges etc.

Regards,

Jon