Dear Ralph (rland)

I suppose, that You have read the above post of WBD about Grundig and Collat. Now I am sure that Your cartridge is not the 10.75x65R Collath and more than that, it may not be the 10.75x65R Grundig too. I begin to suspect that may be You have the same cartridge as me (11x65R Forgotten).

Fist of all about measurement. The dimentions of formed brass are a little less than chamber. Depends on casting material the dimentions of chambercast may a little differ from the chamber or fired brass (also less). So all the measurements are not the absolute. The chambers in old guns also may differ. Because they were produced many years ago by different gunmakers using different tools and usually different technical standards of quality. The same cartridges, but from different producers also may have a little different dimentions (especially old cartridges).

Let’s compare (in inch).
Your base diameter is 0.482, but my 0.494 (not less)
Your neck diameter is 0.471, but my 0.465 (or may be 467)
Not so big difference. I suppose that it may be not significant.

I think that the bore measurement is more important.
You write about bore diameter 0.433.
Please precise it. Is it land (minimal) or grove (maximal) diameter?
If it is maximal so You have really the same caliber as me.

Are Your bore shape more or less similar to my?
Are the land width and grove width equal?
How many lands 6 or 8?
Right or left?