Most likely a J.P. Sauer made gun. The date code is well past the Lindner made gun period, having been proofed in May of 1930. And many think it likely that Sauer made or had a big part making many of the Lindner guns. The initials, if on the underside of the barrel are probably those of the barrel maker/borer.

When an old man dies a library burns to the ground. (Old African proverb)