Most Model 39s (59s too), have six groove rifling with a twist of one turn in 10 inches. Around serial number A200000 the twist was changd to one turn in 18 3/4 inches, supposedly to enable the barrels to be made on the same machinery making 38 Special barrels. The early barrels are pretty tight, with groove diameters about .355" or .356". Does anyone know the groove diameter of the later, 5 groove barrels? I'd like to size my cast bullets to match the groove diameter. I suppose I could shoot the later barrels with .356 and .358 diameter bullets and see which shot better, but I'd rather know the bore diameter I'm dealing with.
Model 39 Bore Dimensions
Linear Mode
