I understand that if you are going to a smaller caliber, you only need to replace the barrel and mag. I've seen videos on you tube where this resulted in some failures to feed. However, due to the not so scientific nature of the videos, it was impossible to tell if the problem was ammo related or the incompatibility of the slide with the 9mm cartridge. I will only do this if reliability is not diminished.
M&P 40 to 9mm conversion?
- Thread starter Mark40
- Start date
Register to hide this ad
First you need a .40-9mm conversion barrel not a regular 9mm barrel. The problems sometimes encountered like FTF and FTE are caused by the heavier weight of the .40 slide. This can usually be resolved by using more powerful ammo or find a brand that works well and/or changing the recoil spring.
Magload
US Veteran
I received the wrong Storm-Lake barrel I got the regular 5" threaded 9mm barrel dropped it in my 40 CORE and ran about 200 rounds through it so couldn't send it back. It was find till I screwed the comp on it then it wouldn't eject. With heavy loads failed about once out of 5 shots even with the heavy loads. Remove the comp shoots good with 115gm plated FP and 3.9 gn on Titegroup. I liked the barrel and comp so just bought a Pro 9mm. It doesn't eject either and a manf of comps says it need a lighter recoil spring to run the comp. i just got a 13 lb but the gun is in the shop getting a Apex Competition kit put in. I will let you know how that spring does.
To the best of my knowledge S&W does not make conversion barrels. You would have to buy from Storm Lake, Bar Sto, KKM or Lone Wolf. You can put a S&W factory .357 Sig barrel in without changing anything but S&W doesn't make .357 Sig barrels anymore as far as I know.
Last edited:
Bkreutz
US Veteran
If you're shooting minor with a comp, you need a 10# spring for the gun to cycle, an 11# is hit or miss (about 80% cycling, and about 5% locking the slide back after the last round). With my major loads(7.0gr AC, 124 bullet) I run a 15# spring, anything lighter is punishing
Bkreutz
US Veteran
Cheaper and Guns are not a good mix. I don't know what the differences are because I don't shoot .40, but a lot of members have done both routes, factory/aftermarket stock barrels or the conversion barrels. I think the only way to see if there is any difference would be to have one of each and measure everything carefully. What I am saying is don't let price be your guide when it comes to buying gun parts. Most of the time you'll be ok, but then again, failures can be painful.
I guess I should have said "less expensive" I don't consider original S&W parts to be inferior. I'm just gathering information at this point, so I don't waste time and or money. I've actually heard of the same issues with Lone Wolf and OEM barrels. In both cases the evaluation process was flawed. I suspect that with decent defense ammo, either would work.
mustangman
Member
The reason I would use the conversion over the stock is because the conversion is made to fit the slide like the factory 40 barrel, while the factory 9 would be a hair loose in the cutout. It may work fine and never be a problem, but why chance it when there are better alternatives.
I guess the question is, would you buy and trust a brand new gun that had a barrel with side to side play in the slide? If factory tolerances are not big deal, then the factory 9 barrel will be just fine.
I guess the question is, would you buy and trust a brand new gun that had a barrel with side to side play in the slide? If factory tolerances are not big deal, then the factory 9 barrel will be just fine.
I have a M&P 40c as my EDC. Based on reading a lot of internet posts that included caliper dimensions of both barrels, I bought a 9mm compact barrel (S&W factory replacement) and 12 round mag. The main difference in the two barrels is the breech face geometry. The tangs on the 40c barrel that lock up into the breech face of the slide are larger than the tangs on the 9mm barrel, so the 9mm barrel fits into the 40c slide breech face (but not the other way around). I have shot a couple hundred rounds with no FTF or FTE. I only use this at the range, for practice (9mm ammo being less expensive than .40 S&W). If I had to do it over, I would spend the money on .40 ammo and practice with that.
Using a non-conversion barrel is not recommended but many people have used them without a problem. You are right about the ammo and I've never seen the point in practicing with ammo that is not very close to my carry ammo.
I'm not a gunsmith, but according to our local competitor/gunsmith, you risk a problem anytime you put in a new part. We have several people who like having multiple barrels, and after a couple of real messes, most in our club will have the gunsmith check the new barrels and fit as needed.
If you put a stock 9mm barrel in the .40 FS M&P, you get a slop fit of about .060, but most work OK. If it does not work, you can't easily add material, and you can expect S&W to tell you "it doesn't belong in a .40."
Even a couple of expensive "conversion barrels" have been trouble, but at least the aftermarket barrel company has an interest in trying to get it to work. One required 3 tries.
So if you want a guarantee that your new barrel will not affect reliability, I suggest you have it installed or at least checked by a competent gunsmith. Remember the corollary to Murphy's Law: Drop in parts don't!
someone mentioned the "heavier weight" of the .40 slide. Has any one compared the weight of a .40 and 9mm to see if there is actually any difference? The recoil spring is the same, at least they both have the same S&W stock number. The barrels have exactly the same external dimensions with the exception of the little tang around the loaded chamber viewing hole. The .40 is 0.026 wider than the 9mm, but that area does on affect lock up. I just got a stock 9mm barrel for my .40, it locks up perfectly. I hope to put some rounds through it Sat AM. I don't suspect there will be any problems. I'll get back to you if there are.
Attachments
uechikid
Member
Conversion barrels are only recommended by the companies that make the conversion barrels. All three of our M&Ps are 40s with factory 9 barrels. They have run flawlessly for thousands of rounds.
The problem is finding a factory barrel. You might call S&W and see if they will sell you one. I have read that they won't but last November they sold me one so I guess it depends on who you talk to at S&W. If you do call them don't tell them you want to convert a 40 to 9.
The problem is finding a factory barrel. You might call S&W and see if they will sell you one. I have read that they won't but last November they sold me one so I guess it depends on who you talk to at S&W. If you do call them don't tell them you want to convert a 40 to 9.
I finally got to shoot my M&P 40 with the 9mm barrel. It work perfectly through a box of 50 115 grn FMJ rounds. I used an aftermarket 9mm magazine. The only difference I saw, other than recoil, was that the 9mm grouped a little tighter.
rsrocket1
Member
^^^My experience exactly. I got a factory 9mm barrel a couple of years ago. It was the old style, slow twist and yes it does wiggle a bit more than the 40 barrel when there is no cartridge in it. With a cartridge loaded (full or empty case), the barrel locks solid in the slide with zero wiggle. I've put several thousand rounds of 9mm through the M&P40 (compared to a couple dozen k of 40) and the big difference is that I am more consistently accurate with the 9mm setup than I am with the stock 40 setup 
uechikid
Member
If you are considering this, and can find a 9 barrel at a reasonable price, you should probably do it. Magazines are plentiful a very reasonably priced. 9mm ammo is so cheap now you can save some at the range. Not to mention, if you take new shooters to the range, 9mm is a good caliber for them.
I fail to understand the fascination of 9mm barrel in the 40....if I need a 9mm I buy a 9mm...
On more than one occasion I have seen fellow USPSA/IDPA competitors come to the line with the wrong barrel... or more correctly wrong ammo for the barrel in their gun!
I know...(it's like having two guns in one)....might work for you but not me..
Randy
On more than one occasion I have seen fellow USPSA/IDPA competitors come to the line with the wrong barrel... or more correctly wrong ammo for the barrel in their gun!
I know...(it's like having two guns in one)....might work for you but not me..
Randy
Similar threads
