A seller has a nice Peruvianicon 1935 model FN Mauser converted to .30-06.

A number of these conversions were done by FN rebarrelling from the original 7.65x53mm caliber. Many others were done by Peruvian arsenals by just rechambering the original barrel.

The problem is the two processes produce markedly different results. The rebarrelled guns have an excellent reputation for accuracy. The rechambered guns do not, due to the original barrel diameter being .312" instead of the rebarrelled guns .308".

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