FS M&P Barrel swaps

[CNobbe]

I am looking to buy a used full size M&P in .40 locally, great price police trade gun with minimal use.

I've been searching around, and believe that yes, you can drop an M&P 9mm barrel in the .40 and it'll function fine as the dimensions are all the same.

I know storm lake makes conversion barrels for M&Ps, and could go that route too. I've been using a Lone Wolf barrel in my Glock 27 for a long time.

Basically just looking for some caliber conversion clarity with the M&Ps. I'm not sure why I haven't considered them in the past, but it seems the triggers have been improved...

 

[tcanthonyii]

From what I've read since purchasing a 9c a month ago is that yes you can drop a 9mm barrel into a 40 and even use the 40 mags! Obviously I have no way of testing this.

The triggers are not improved, unless you go with a pro, However Apex makes great drop in parts and you can replace the whole setup for just over 100.

The same guy I bought my 9c from had a 40 pro, I'm positive 320 could have purchased it.

 

[jhb]

While I'm no gunsmith...the hole in the 40 slide is going to be much bigger than the 9mm barrel. Plus the barrel hood and breech interface are different sized. This affects lock up and stops an oem 9mm barrel from locking up properly in a .40 pistol. It also affects accuracy. This has been covered over at the s&w forum and m&p shooters site many times. There is those who do it and say no problems and those who say don't and why you shouldn't including s&w. You can drop in a .357 sig into a .40 and s&w says that is okay. In the end...... Do at your own risk.

The safe way is to buy a true conversion barrel that accounts for these dimension differences and keeps things right and safe. Too each their own though.....

 

[Walt Sherrill]

I've got both a 9mm and .40 M&P Pro... but never tried swapping the barrels to test functionality.

While the barrels of the M&P Pro in 9mm and .40 do seem to be the same diameter (something that Witness used to do with their small-frame 9mms and .40s), I don't know how well they'd function when swapped for the breech face and extractor function reasons cited above by jhb.

Given that the price of a factory barrel and the price of a conversion barrel will be similar I'd just get a CONVERSION barrel and not worry about the "function" question -- I've had a number of conversion barrels over the years, and they all worked as they should!

 

[wally]

While the barrels of the M&P Pro in 9mm and .40 do seem to be the same diameter (something that Witness used to do with their small-frame 9mms and .40s), I don't know how well they'd function when swapped for the breech face and extractor function

I've an M&P 40c an M&P 9c replacement barrel that functions fine in the 40c although I had to use 9mm mags to get the reliability I demand. Its a nice setup, .40 for carry, 9mm for less expensive practice. The "slop" in the barrel hood from the 9mm barrel in the .40 slide seems to have no significant effect on accuracy as I don't need to adjust the red dot sight when I change barrels -- an unexpected plus.

I've also used a Storm-Lake threaded 9mm conversion barrel in an M&P40 and again there was no significant POA/POI change shooting steel plates at 10 yards.

I've since got an M&P 9 C.O.R.E pro-series pistol and have milled the barrel hood on the S-L barrel to fit the 9mm slide and again no significant shift shooting suppressed with the S-L barrel or unsuppressed with the original at 10 yards.

In the case of the M&P it appears the only thing the "true conversion" buys you is a proper fitting barrel hood which seems to make little to no difference in the way the barrel and slide lock up. The Storm-Lake barrels run 2-3X the S&W replacement barrel cost from Brownells or Midway.

 

[Walt Sherrill]

n the case of the M&P it appears the only thing the "true conversion" buys you is a proper fitting barrel hood which seems to make little to no difference in the way the barrel and slide lock up. The Storm-Lake barrels run 2-3X the S&W replacement barrel cost from Brownells or Midway.

I had no idea that factory barrels for an M&P (or MY&P Pro) would be that much cheaper than a conversion barrel. I'm used to spending about $100 for any of them (+/- $30), so a factory barrel for $40 - $60 makes it an easy choice.

 

[CNobbe]

Going to test out a factory 9mm barrel in my 357 tomorrow. After installing it and checking it over, it does drop in with extremely little play anywhere.

 

[ChrisMG]

I do this with my 40 (factory 9MM barrel as drop-in a 9MM mags). Accuracy isn't that great though. I'm not sure if it's because of S&W's earlier issues with accuracy out of the 9MM or some other reason.