S&W CS says M&P 40 to 357 sig conversion unsafe.

[Oldsalt66]

Same frame, same firing pin, same recoil spring assembly, same striker, same magazine.....same internal parts, although I can't swear for the locking blocks being identical.

Has anyone heard of any real world issues regarding this matter ?

I, myself, have not and I've been messing around with polymer M&Ps since their introduction, which btw, was in .40 S&W making them robust pistols.

ETA:

The following pertains only to legacy models and not the 2.0 line with which I have no experience.

You can replace the barrel of an original model .40 S&W M&P with a factory 9mm barrel and the result will be a perfectly shootable pistol.

However, the opposite is not true; you cannot replace the barrel of a 9mm M&P with a factory .40 S&W barrel.

The conversion between .40 and 9mm goes only one way; .40 to 9mm.

 

[Ruger Nut]

I have a LE trade in M&P .40 with a .357 SIG barrel in it. I have been shooting it now for over 3 years without ANY problems. I must be living on the edge.

 

[bugoutbegone]

Smith & Wesson

First off Gun owners do your own research I am just from the range s&w 2.0 magazine field test on my s&w .357 sig not only will this firearm convert the 9mm mags load .357 rounds and there is a smooth release. so those that use this plateform to mislead shame on you

 

[peh_7]

S&W has changed their story!!! Shortly after buying my M&P 40 in 2009, I called S&W to ask if a .357 Sig barrel would work in my pistol and if they had any available. I was told yes and yes, and purchased an original S&W .357 Sig barrel from them for the M&P 40. I also have a 9mm conversion barrel and magazines for the pistol. I have fired many rounds in all three calibers through the pistol with NO problems. To do this you must start with an M&P 40. At least with the 1.0 M&P the 9mm "bolt" face is too small to accept the rim of the .40 and 357 Sig.

 

[Racer X]

If you are REALLY concerned about the pressure/stress of .357 SIG, get the new 10mm model, and a .357 SIG barrel when someone makes them. That's my plan. Just swap for the right recoil spring.

Once I start reloading, I'm going to get a .357 SIG barrel for my 1911a2 10mm. Already got a SIG .357 SIG barrel for my P229 in .40

 

[colt_saa]

First off Gun owners do your own research I am just from the range s&w 2.0 magazine field test on my s&w .357 sig not only will this firearm convert the 9mm mags load .357 rounds and there is a smooth release. so those that use this plateform to mislead shame on you

Normally my first response to a New Poster is "Welcome to the Forum"

I think I will skip that tonight

Ignoring the poor grammar of your statement, is your first post to a new Forum really intended to start some kind of chambering argument?

 

[swsig]

This is an ancient thread, but since it has been revived, I'll add my $.02. I have a 1.0 M&P 40c. After it had fired over 13,000 rounds of .40 S&W, I converted it to .357 SIG using a Storm Lake (R.I.P. ) barrel. Since then, I have fired over 2,800 .357 SIG rounds, and my 40c is holding up well.

 

[rosewood]

Once I start reloading, I'm going to get a .357 SIG barrel for my 1911a2 10mm.

Why not go with a 9x25 dillon instead and get another 200fps

 

[Kinetic_Transfer]

the ONLY difference between the .40 version of the M&P and the .357 SIG version is the barrel. Period.

Some gunmakers use the same slide for a number of different models

Quoted for recognition.

Same slide. Same frame. Same spring. Same internals.

Having owned the first-gen M&P 357 SIG as well as my current M&P 40 2.0 with an aftermarket 357 SIG barrel, my experience has led me to believe that Smith and Wesson intentionally designed the 40 to withstand the 5,000 psi difference in cartridge pressure that the 357 SIG acquires.... but they can't legally give credence to any post-manufacturer modification of their firearms, especially when it comes to internal pressure differences.

Nonetheless, even if the original 357 SIG slide was slightly thicker gauge steel than the 40 slide (which it isn't), the worst that would happen is you'd probably end up cracking the 40 slide at like 30-40K rounds vs 60K with the thicker slide.

Just my opinion, but with all of the aftermarket 357 SIG barrels that have been dropped into M&P 40's throughout the years ..... we would have heard about any widespread catastrophic failures by now. Heck, I haven't even heard of any and certainly haven't experienced any after well over 20K rounds.



~

 

[Kinetic_Transfer]

Flatter shooting for self defense? Non-issue out to 50 yards.

When there's an active shooter and you have to place your shots beyond 50 yards .... Are you actually implying that a flatter trajectory wouldn't be an advantage?

Higher velocity with deeper penetration? Not needed compared to other catrtridges with modern bullets meeting SD requirements.

Higher velocity not needed? Maybe.

Advantageous? Unequivocally.

Aside from the 357 SIG throwing rounds at twice the speed of sound with 600-700 ft-lbs of kinetic energy at the muzzle.... the terminal wound ballistics as a result of these significantly higher velocities are where the 357 SIG outshines most.

Expensive.

Yes.

Hard to find.

Yes.

Limited loading choices.

50-147 grains is plenty to elicit devastating wounds.

More recoil and blast

It's only got 2,500 more psi in cartridge pressure than the 10mm. The higher recoil is negligible. The muzzle blast is definitely more noticeable, but it's nothing that ever made an impact on my own shooting.

making it harder to shoot well and fast.

No. Just no.

Eats up gun and shooter.

lol

Lower capacity vs 9 mm.

15+1 is more than enough.

What's to like?

Everything except the price.

And now with the pandemic ammo shortage, it's even harder, but the weapon itself is a sensational one. The terminal wound ballistics don't lie.

 

[CB3]

Kinetic_Transfer:

This thread is about giving people information to make potential life and death decisions, particularly regarding the .357 Sig cartridge.

The question is: does the undeniable increase in terminal performance of .357 Sig come at too high a cost? The Market, not just my opinion, has said yes, the cost is too high. This is not now and never will be a popular self defense cartridge.

The overall expense of these increased terminal wound ballistics have been noted by the federal government, by state agencies, counties and local agencies. Their resounding rejection of this cartridge prove the cartridge is not desirable for the vast majority of professionals who carry pistols for work.

The buying public also agrees the juice isn't worth the squeeze. Loads and bullets in common, less expensive, more readily available defensive cartridges have progressed to where they all perform similarly and adequately, given all the parameters required for self defense cartridges.

There is a small cadre of civilian devotees of .357 Sig, that is true. Yet as potential new adopters look at this cartridge, there is little to persuade them to get into it. Standard defensive calibers and cartridges are peaking in all-time popularity.

There is a host of calibers/cartridges that have adequate terminal performance in the hands of a trained shooter. Depending on increased terminal performance as a fight stopper is less important than other factors.

Winning a gunfight is usually predicated on three factors:
1. Being the first to get a meaningful hit
2. Bullet placement on the target
3. Placing a good number of effective rounds on target quickly.

High pressure, big blast, heavier recoiling cartridges like .44 Mag., .357 Mag., 10mm, .357 Sig, often produce poor shooting and slower follow-up shots. Major flinching is common when trying to shoot fast. Today people are trending toward carrying smaller guns which are even harder to manage with high pressure cartridges.

Self defense gun and ammo choice is always going to be a compromise based on individual needs and abilities. .357 Sig works for a few people. It is not the choice of the clear majority of defensive handgun carriers. Your priorities and claimed abilities justify your use of the cartridge. That doesn't make you wrong. You are just in a super-minority.

 

[rosewood]

Aside from the 357 SIG throwing rounds at twice the speed of sound..

Not exactly. The speed of sound is roughly 1125FPS and varies depending on altitude and pressure. You may be thinking speed of sound is over 700 MPH. Twice the speed of sound would be over 2200 FPS. You might get that in the sig with a super light bullet, but with a 124 grain, you can get just over 1400 FPS. I did hit over 2200 FPS with a 68 grain Lehigh bullet in the 9x25 Dillon.

Agree with the rest of your post however.

Rosewood