wow6599
Member
I need some info on converting a S&W M&P 40 to a .357 sig. I have read that the punishment from a .357 sig will wear out a gun fairly quickly - .40 @35,000 psi and .357 @ 40,000 psi. Any thoughts or answers? Thanks All.
.357 sig conversion?
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I don't think I have ever heard that before. I think the biggest issue was in rechambering 9mm guns for .40, the rounds are almost identical in pressure, but the .40 is throwing a heavier bullet at the same speeds, so the forces involved were a little too much for some of the initial .40 handguns. I don't know which ones, but that is what I thought the issue was.
threefeathers
member
I have both 40 and 357Sig barrels for my 229 and HK P2K.
First I've completely converted to the 357Sig probably for the same reason nearly 200 LEO agencys have. It is one of the most inheriantly accurate rounds you will ever fire. The bottleneck design wants to feed.
I've found a reloading formula that I can tuen out 350 rounds an hour on me RCBS Pro 2000.
BUT, a cavaet, I have had to put MMC adjustable sights on all slides.
Why, the fixed sights from Sig and HK are set up for the 165 gain 40. The 357 Sig is best fired with the 125 grain pill. The lighter bullet strikes 4-5 inches lower. With fixed sights I take a 1200 hold, with 40 a center hold. For my carry gun I want dead on so I put the 40 barrels away and put the new MMC sights on both guns.
First I've completely converted to the 357Sig probably for the same reason nearly 200 LEO agencys have. It is one of the most inheriantly accurate rounds you will ever fire. The bottleneck design wants to feed.
I've found a reloading formula that I can tuen out 350 rounds an hour on me RCBS Pro 2000.
BUT, a cavaet, I have had to put MMC adjustable sights on all slides.
Why, the fixed sights from Sig and HK are set up for the 165 gain 40. The 357 Sig is best fired with the 125 grain pill. The lighter bullet strikes 4-5 inches lower. With fixed sights I take a 1200 hold, with 40 a center hold. For my carry gun I want dead on so I put the 40 barrels away and put the new MMC sights on both guns.
RobMoore
Member
I wouldn't think you'd need to do anything more to covert it than swap barrels and put a stronger spring in it. I don't think the .357SIG will wear it out any quicker (that you would notice). At 50k rounds through my issued P229 in .357SIG I had only had small parts here and there replaced (springs every 5-6, takedown lever broke @ 35k, trigger return spring @ 45k). They replaced it around 50k just because its a duty gun and they said it could critically fail at the wrong moment from then on. I didn't argue with getting a new gun, but I think it could have continued twice as long or more.
EDIT: Every one of those 50k were 125g Gold Dots @ 1350fps (give or take).
EDIT: Every one of those 50k were 125g Gold Dots @ 1350fps (give or take).
strangelittleman
Member
There shouldn't be any problem, the only difference in the M&P40 and the M&P357 is the barrel and stronger recoil spring.( sorry I don't have the springs weights handy) the mags and all other parts are the same.
The New Mexico State Police are in the process of transitioning to the M&P357 and seem to like it well enough.
My fmr Sgt. bought a Sig P226 conversion set NIB in .40 w/ a factory .357 barrel for his second job at the local college campus police, has used both barrels with the same spring( only one supplied from factory) with no problems and yes he did call Sig to ensure it was safe to do so, their answer was "absolutely!"
The New Mexico State Police are in the process of transitioning to the M&P357 and seem to like it well enough.
My fmr Sgt. bought a Sig P226 conversion set NIB in .40 w/ a factory .357 barrel for his second job at the local college campus police, has used both barrels with the same spring( only one supplied from factory) with no problems and yes he did call Sig to ensure it was safe to do so, their answer was "absolutely!"
jdh
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The part numbers for both the 40 and 357 recoil spring assy are the same. The frame is the same for both the 40 and the 357. The only difference between the slides are the caliber stamp on the M&P logo. The mags are stamped for both the 40 and 357.
Change the barrel, shoot it, and don't worry about it. I have been for about 150 rounds now. Slide says 40 barrel hood says 357. Shoots just a bit low with 125 grain Gold Dots out to 25meters. Other than that all is well.
Change the barrel, shoot it, and don't worry about it. I have been for about 150 rounds now. Slide says 40 barrel hood says 357. Shoots just a bit low with 125 grain Gold Dots out to 25meters. Other than that all is well.
RobMoore
Member
The factory may stipulate the same spring for both, but I'd go for a lb or two extra.
Well,jdh,apparently they've changed their stance in the past few months.When I called,I was told they absolutely would not sell me a barrel to do that conversion.Their answer was that if I wanted a 357sig model,then I should've bought that in the first place.Never mind that it wasn't available at the time I got my 40 model...
You say packing list,meaning you got one,how much was it?I guess I'll have to call them again...
Cool,that'll be 7 dual-chambered pistols...
You say packing list,meaning you got one,how much was it?I guess I'll have to call them again...
Cool,that'll be 7 dual-chambered pistols...
jdh
Member
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Midway list them cheaper but never has them in stock. They are $92+shipping. Call the parts department not customer service and give them the part number. Don't ask for the barrel by description.
BTW, it was a drop in swap, accuracy was good, and function was perfect.
BTW, it was a drop in swap, accuracy was good, and function was perfect.
OP
OP
wow6599
Member
S&W says NO!
Over the weekend I bought a 357 sig barrel for my M&P40. Today I called S&W to see if I needed a stronger spring and just double checked to make sure the barrel "drop in" was all I needed. S&W's customer service rep said they "are not even compatible" and that companys that sell the barrels for conversions need to stop because they won't work. I stated that it was a factory barrel and her reply was" no, they won't work together". Is this b.s. to sell more guns or is there any truth to it?
Over the weekend I bought a 357 sig barrel for my M&P40. Today I called S&W to see if I needed a stronger spring and just double checked to make sure the barrel "drop in" was all I needed. S&W's customer service rep said they "are not even compatible" and that companys that sell the barrels for conversions need to stop because they won't work. I stated that it was a factory barrel and her reply was" no, they won't work together". Is this b.s. to sell more guns or is there any truth to it?
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