9mm Barrel for my M&P .40 full size?

drew-67 · Dec 12, 2014

Hi, I seen a couple posts pertaining to the fact that you can convert a 40 S&W to 9mm by changing out the barrel..So now I am thinking this may be a good option as I've never had or shot 9mm. So anyway looking for some help..
What are the advantages for getting a 9mm? Also I see the Barrels from Storm Lake are $150 or more..Are there alternatives? Seems like if I spend this much for barrel and then what about a new 9mm magazine or two..I am looking at a good amount of money that could go towards a whole new gun??
Please point me in the right direction..Thanks!

Rowlette · Dec 12, 2014

I used S&W OEM 9mm, 40 on my .357 MPC all works well. Not sure it you are able to purchase them anymore but it was very cost effective. Yes you need replace magazines but that is very low cost.

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Rastoff · Dec 12, 2014

I got a factory 9mm barrel for my full sized .40S&W. I then found two 9mm mags and I was in business. I think it would be worthwhile to replace the recoil spring as well because the ejection is a little weak when shooting 9mm. Even so, the gun works as a 9mm.

I got a factory barrel from Midway USA for about $70. I got the mags used for about $40. So, for about $110 I have a new gun.

The question now is, is it worthwhile to do it? Well, if you want a 9mm this is the least expensive way to get a good one. That said, there's nothing wrong with the .40S&W round. 9mm is a little less expensive to shoot. That's the only real benefit to switching to 9mm.

drew-67 · Dec 12, 2014

Thanks..that would be about half the cost and would seem more sensible (unfortunately checked Midway and out of stock/no back order)..
I would certainly be tempted to give 9mm a try for that cost..Anyone know any vendors that have them in stock?
Why are the conversion barrels so much more?

mustangman · Dec 13, 2014

Even if you went with the $150 conversion, you can get mags from Quantico for 29.95 each, or 3 for 78.00, and have an M&P FS 9mm for about 250.00. If you're just looking to save on ammo, that would take a while to recoop, but if you want a 9mm, just to have a 9mm, then you're not going to find a better gun at a better price than that.

Bkreutz · Dec 13, 2014

S&W M&P 9mm Full Size Barrel at G and R Tactical

MyDads38 · Dec 13, 2014

Out of curiosity, if you already have a 9mm M&P, can you do a 40 S&W barrel/mag change with same results? or would you also need to change out recoil spring too? Thinking it might be beneficial to be able to convert from one caliber to another, if ammo becomes hard to find again.

Will the conversion be as accurate?

03Fatboy · Dec 13, 2014

MyDads38 said:
Out of curiosity, if you already have a 9mm M&P, can you do a 40 S&W barrel/mag change with same results? or would you also need to change out recoil spring too? Thinking it might be beneficial to be able to convert from one caliber to another, if ammo becomes hard to find again.

Will the conversion be as accurate?

Yes, has anybody done this?

drew-67 · Dec 13, 2014

Bkreutz said:
S&W M&P 9mm Full Size Barrel at G and R Tactical

Thanks for the link! Unfortunaty when I tried to place order from cart it showed unavailable and no back order..
Anyway, has anyone had a chance to compare both options? I can get the conversion for $150 with free shipping,, the one in your link was $99 plus shipping cost... so about. $40 difference. Not a lot if the quality and fit is better.
I still like the sounds of Midway though ( around $75.00).. But if not available then, I guess not an option

ironhead7544 · Dec 13, 2014

Looks like you can convert the 40 S&W version to three different rounds in one pistol easily. Looks good to me. Easier to find ammo that will work.

Might have to look into this.

Bkreutz · Dec 13, 2014

drew-67 said:
Thanks for the link! Unfortunaty when I tried to place order from cart it showed unavailable and no back order..
Anyway, has anyone had a chance to compare both options? I can get the conversion for $150 with free shipping,, the one in your link was $99 plus shipping cost... so about. $40 difference. Not a lot if the quality and fit is better.
I still like the sounds of Midway though ( around $75.00).. But if not available then, I guess not an option

Give them a call, their online ordering system is flakey

. I didn't do a .40 to 9mm conversion but I did put a KKM replacement barrel in my 5" Core. I didn't notice any improvement in accuracy and speed, but I don't shoot heavier bullets (over 130gr) so I wasn't expecting much difference. HTH

Jiman · Dec 13, 2014

MyDads38 said:
Out of curiosity, if you already have a 9mm M&P, can you do a 40 S&W barrel/mag change with same results? or would you also need to change out recoil spring too? Thinking it might be beneficial to be able to convert from one caliber to another, if ammo becomes hard to find again.

Will the conversion be as accurate?

You can't do it IIRC. The breach face on the 9mm slide is too small to fire the larger 40 cartridge.

Rastoff · Dec 13, 2014

MyDads38 said:
Out of curiosity, if you already have a 9mm M&P, can you do a 40 S&W barrel/mag change with same results? or would you also need to change out recoil spring too? Thinking it might be beneficial to be able to convert from one caliber to another, if ammo becomes hard to find again.

Will the conversion be as accurate?

Jiman said:
You can't do it IIRC. The breach face on the 9mm slide is too small to fire the larger 40 cartridge.

Actually, it can be done, but it's not as easy. Jiman is correct and the breech face on the 9mm slide is a little smaller than the .40S&W is. If you get a .40S&W barrel, the sides of the hood can be filed down a little and it will then fit.

uechikid · Dec 13, 2014

Call S&W to see if they have any in stock. I've have had a 9c barrel on back order with Midway for months and was getting tired of waiting so I called S&W. They had some in stock for $72 so I ordered one. I don't know if they have the FS 9mm barrels but it's worth a phone call.
This was last week.
We have 9mm barrels for all of our M&P 40s. When I take new people shooting I start them off with our M&P 22 then move them up to the 9mm. It's a good progression for newbies.

Johnmuratore · Dec 13, 2014

I've got the .40 to 9mm conversion barrel from KKM Precision and it works great in my 40c. I know it'll take me a long time to make up the cost by the savings in ammo, but my wife and I are learning to shoot semis and I thought the 9 would be easier to learn with than the 40.

Linejudgemick · Dec 13, 2014

I got a 9mm barrel from Midway yesterday that has been on backorder for right at a year. I already have a full-size 9mm magazine that I use for my 9C with an X-Grip. Haven't had a chance to use them yet, but I'm looking forward to giving them a test drive tomorrow.

Jiman · Dec 13, 2014

I think the biggest advantage of a barrel swap vs getting a new gun, is that all the mods, and tweaks carry over. You have the same trigger, sights, and feel...not to mention all the $$$ you'd have to spend in aftermarket part if you got a new gun.

If you own a 100% stock gun, it might be cost effective to get a whole new gun.

rsrocket1 · Dec 13, 2014

Jiman said:
I think the biggest advantage of a barrel swap vs getting a new gun, is that all the mods, and tweaks carry over. You have the same trigger, sights, and feel...not to mention all the $$$ you'd have to spend in aftermarket part if you got a new gun.

If you own a 100% stock gun, it might be cost affective to get a whole new gun.

Or if you have an M&P40 with the Apex FSS kit, you can see what an M&P9 with an FSS kit would shoot like.

If you reload, a 180g 40 S&W bullet with 3.0g Red Dot or Clays will let you know what an M&P9 feels like with 1100 fps 120g bullets at an even lower cost.

MyDads38 · Dec 13, 2014

Rastoff said:
Actually, it can be done, but it's not as easy. Jiman is correct and the breech face on the 9mm slide is a little smaller than the .40S&W is. If you get a .40S&W barrel, the sides of the hood can be filed down a little and it will then fit.

Thanks for the response. I'm not interested in "making" my 9mm work with a 40 cal. barrel, especially having to file things to get them to fit. I was just curious

Seems to me, S&W would put together a combo set, pre-packaged with a frame and the 40, 9mm and 357 Sig barrels/mags for purchase; kind of like a Dan Wesson kit, but to change calibers, not barrel lengths. Just a thought....

Rastoff · Dec 13, 2014

MyDads38 said:
Seems to me, S&W would put together a combo set, pre-packaged with a frame and the 40, 9mm and 357 Sig barrels/mags for purchase; kind of like a Dan Wesson kit, but to change calibers, not barrel lengths. Just a thought....

While it might seem to make sense, it's more complicated than it appears.

Remember how I said that the .40S&W barrel hood would have to be filed down to fit the 9mm slide? Well, that means the 9mm barrel hood doesn't fit the .40S&W slide well; it's a little loose. This means that a .40S&W gun, converted to 9mm, is not as good as it could be. So, a .40S&W barrel, fitted to a 9mm slide will actually be a better conversion. This is also why an after market .40S&W to 9mm conversion barrel is better than just dropping in a factory 9mm barrel.

Now, that all depends on what you want for precision. I can testify that the factory 9mm barrel works in a .40S&W slide because I have one. I have not tested it to see just how precise it is. I only know that it's good enough to use as a defensive gun which is to say not very precise.

9mm Barrel for my M&P .40 full size?

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