Peruvian 1935 rebarrelled or rechambered? How to tell without slugging the barrel?

[vintage hunter]

The question is how to tell which caliber conversion method was used without slugging the barrel?

Measure the groove diameter at the muzzle end with calipers.

Try a bullet in the muzzle. If it's 7.65 it'll disappear right to the brass.

If it has good rifling right to the end it won't. A .30-06 round in the muzzle of a 7.65mm Argentine 1891.