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S&W M&P 40 question.
Horse Plains Drifter
Forums Admins, Member, Moderator Posts: 39,372 ***** Forums Admin
I have the idea to switch a M&P 40 over to be able to fire 9mm. My research shows that I just need a 9mm barrel and magazine. I have also read a couple posts that state that the 40 mag. will even work, but may not function correctly. Am I on the right track here? TIA for any input.
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http://www.brownells.com/handgun-parts/barrel-parts/barrels/s-w-m-p-barrel-conversion-prod40296.aspx
But yeah, that ought to do it. Edit: Might be some advantage in swapping recoil springs, too. . .you can try it and see if you need to.
You very well may be able to get 40SW magazines to work.
Back in the Clinton standard cap mag ban era, some people used 40SW mags in their 9mm guns to cram in an extra 1-2 rounds. This can work, though I'd say 9mm M&P mags are cheap and readily available enough that you should just buy one.
I bought a 9mm barrel from Lone Wolf. Installed it in my Model 27. Functioned OK, even using Model 27, 40 caliber magazines. The only problem I recall, with using 9mm in G 27 40 caliber magazines. Is it had FTF jambs, with 147 grain H-P's with large diameter flat noses.
Have you considered getting a replacement/swap-out barrel in .357 Sig instead? I have them for all of my Sigs (226,229,239) and the .40 barrels sit in the safe. Use the same mags and the slide face is identical because they use the same case head. The .357 will give you about 2-300 added fps with a given bullet weight. I get my barrels from BarSto Precision.
Depending on load, 357 SIG *can* get you around 200 fps more than 9mm loads. But that advantage typically goes down when you look at the BEST available 9mm+P loads. If you're going to do the comparison, IMO, you have to compare expensive 357 SIG loads to "premium" defensive 9mm+P rounds, since the later are probably what you're actually going to using in your gun for defense.
Do that and best commercially available 125 grain 357 SIG rounds get about 1450 fps. But most commercially available loads (eg Federal, Winchester, Speer, Remington, Hornady, etc) get you only 1350 fps. Meanwhile best available 125 9mm+P rounds get you about 1250 fps (CorBon, Buffalo Bore, Double Tap).
So there is a potential 200fps advantage, though realistically maybe not quite that much. At the same time, 357 SIG ammo is generally harder to find on shelves, more expensive, offers more recoil, and lower capacity. (Otherwise known as "there is no such thing as a free lunch"). These disadvantages might outweigh the slight ballistic advantage, depending on user.
If you go up in bullet weight, heaviest available 357 SIG rounds are 147 grain, and will get you up to 1250fps (Double Tap, Federal). The best premium 9mm+P 147 grainers can still get you 1150 fps. No question 357 SIG is better, but is that extra 10% oomph really worth all the other downsides?
Its a little harder to compare directly to 40SW, since bullet weights aren't the same. Yes, 357 SIG shoots faster. . .because its shooting much lighter bullets! Compare "apples to apples" and 357 SIG really doesn't do any better than 40SW at all.
EG: Speer Gold Dot 155 grain 40SW get 1200 fps, and non-premium Federal 155 grainers get you 1160fps. IMO these are functionally identical to the 147gr 357 SIG at 1250fps, yielding effectively identical kinetic energy and momentum.
Comparing to 135 grain 40SWs isn't entirely "fair" since most of those rounds are basically "40sw -P" intended to generate 9mm like ballistics and recoil. But if you do the comparison, the Double Tap 135 grain 40SW yield 1375 fps. IMO that's directly comparable to 1450fps from a 125 grain 357 SIG, with 40SW punching a slightly bigger hole.
Bottom line, 357 SIG shoots the same bullets as 9mm, just a little faster. Whether or not roughly 10% more velocity is worth the tradeoff in cost, capacity, etc, is up to you to decide.
IMO 357 SIG doesn't really generate "better" ballistics than 40SW, it just accepts lighter weight bullets. Makes perfect sense, since its basically just a necked down 40SW to start with! Whether or not accepting a lighter smaller diameter bullet is an "advantage" is highly debatable (some would argue its a disadvantage).
In my opinion, there is no advantage to 357 SIG over 40SW for conventional defensive use. If you're talking about "special circumstances" like hunting, or punching through windshield glass (which is why certain police agencies like this one), or maybe shooting this through a rifle where flatter trajectory might matter, that's a different story.
Had a CZ in 40, for a very short while. Got rid of it pronto. For some unknown reason, the perceived recoil was much harsher than the tupperware Glocks I was use to. Even though the CZ was much heavier, with it's steel frame. The only reason I could think of, was that it's bore axis was higher?