+P in your Model 39? I was developing +P reloads for my 9mm pistols in the late 1970s. A particular load worked well in my Hi Power but when I fired it in a newly purchased a Model 39, the case ruptured down the loading ramp and cracked the grips. What happened?

The answer was bore diameter. Ideally, a 9mm bore should be 0.354 diameter plus or minus a couple thousandths. This particular Model 39 checked at 0.352. By comparison, my Hi Power's bore diameter checked at 0.359. The tighter bore raised my +P loads to dangerous levels.

By the way, because the 9 mm and .38 caliber barrel diameters are so close, manufacturers would use one rifling broach or button for both 9 mm automatics and .38 caliber revolvers. During this era, Smith & Wesson went with the 9 mm bore.

So, before using +P ammunition in your Model 39-2, have your gunsmith slug the bore and check the bore diameter. If it's in the 0.354 range, I would be careful about using +P. Especially do not use the 9mm NATO ammunition that appears on occaision.