Police arrested a 19-year-old university student for building and selling pen guns capable of firing 7.65 mm rounds on Monday.
The suspect, identified as N.M., was detained at a bus station in the northwestern city of Bursa.
He had arrived from Istanbul where he is studying mechanics.
A total of 16 guns were found in his possession.
The suspect told police he also worked as a lathe operator and was in Bursa to contact potential buyers.