1909 Argentine Mauser 7.65 will not close on a GO gauge

[lraklrak]

I recently purchased a 1909 Argentine Mauser in really great shape.
According to the description it is a 7.65 caliber.
I purchased a GO and NO-GO gauge for the 7.65x53 Argentine caliber.
When I go to place the GO gauge in the bolt will not close.
I never had this happen with any of my other rifles up until now.
I have read where many of these were converted to 30-06 years ago.
Is there anyway I could tell if this is a 30-06 instead other than loading a 30-06 and see if the bolt will close?
Any suggestions on this would be great.