I see daniel craig's point, but Speedo66 has 6,000+ posts here, so I figure he just felt he could get better information here faster than by Googling around and separating the wheat from the chaff. I will answer with what I understand to be the case:
30 Luger, aka 7.65x21 and 7.62x25, aka 30 Mauser and also 30 Tokarev, are NOT interchangeable. It is like .308 and .30-06 - the difference in overall length is too great. (The difference in bullet diameter may be purely nominal. That is something else to Google!)
In fact, 30 Mauser and 30 Tokarev, despite being the same size, are not considered interchangeable, because 30 Tokarev is considered to be more powerful.