M&P40 converting to 9 - downsides?

[DanTana]

DocSunShine, I might of received a bad barrel, I communicated with Storm Lake after I received the barrel and took it out shooting. They told me the barrel I got was the "old version" and the "new version" was not being manufactured yet. My M&P was using the "new version" of barrel so the two were not 100% compatible, I was told by Storm Lake. I emailed KKM before I bought one of their barrels and they told me that all their new barrels were using the "new style" and after receiving it I verified it was identical to my .40 barrel. It fit in the slide very snugly and shoots fantastic. I have not had one problem with it. You can look up the barrel differences on the web. The older one has what looks like a collar around the barrel just past the chamber. The new version does not have this. If you have an older version M&P the Storm Lake would probably be your best bet. I was unable to find a stock S&W barrel for it. I included a picture to illustrate the differences between barrel designs. The top is the "old" version, the bottom is the "new" version.

 

[robkarrob]

I have both a 40 and 9mm barrel. I have all the tools for measuring them accurately. The barrels are identical, except for two differences. The bore diameter is larger on the 40, since the 40 bullet diameter is larger than the 9mm. The second difference is the tang width, at the top rear of the barrel, is .026 inch wider on the 40 barrel. Since the 9mm tang is more narrow, it will fit in the tang slot in the 40 slide. The 40 barrel tang will not fit in the tang slot in the 9mm slide, unless the tang width is ground down by .026 inch (.013 per side). A member of this forum did grind down the tang width, and found the 9mm to 40 conversion worked fine, after that modification.

Just for reference, a human hair is about .004 inch thick, so you are dealing with about 3 hairs width on each side of the tang or tang slot, not very much. I have not had a single problem, having fired well over 500 rounds of 9mm, using a stock S&W 9mm barrel in my 40 Shield.


Bob


Photo of the tang widths on my 40 and 9mm barrels: