Converting G27 .40 cal to .357 SIG

With Glocks you might need a different magazine for the best reliability, as I understand the 357 follower is different than the 40 S&W follower. It is mentioned in this article:

https://www.shootingillustrated.com/articles/2019/7/19/converting-guns-to-357-sig-testing-options/

Lennyjoe said:

I went ahead and ordered a Double Diamond barrel from the Glockstore just to give it a try. Seems like they got good reviews and Others like Storm Lake and AlphaWolf barrels are out of stock. I’ll run factory ammo out of the G27/33 conversation for now and see how I like it.

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I have two KKM barrels, for a G23 and G22, both gen4. They work very well, and .40 mags with the '9' or '10' followers have worked flawlessly with .357 Sig. Reliability has been great.

As far as reloading (because you mentioned it), I lube with One Shot in a ziplock, then resize everything I intend to load. Then I roll them between paper towels to get the lube off. I did buy a case gauge for this cartridge, but once the sizing die was set, it hasn't been needed except to double check.

After that everything is done as per straight walled cartridges: I prime, barely flare, seat, and crimp. The crimp doesn't seem too necessary, but I bought the Lee FCD so I ended up doing it anyway.

The way I lube seems to get lube inside the mouth which reduces neck friction a little. So I'm careful about rechambering reloads too much. With new brass, setback hasn't been anything significant. So anything I load for woods carry is new brass, to avoid potential setback issues.

Neck tension can be an issue with bottle-neck pistol rounds, and setback is a potential issue that could raise pressure. One way around this is to use a powder with a high loading density with high case fill. These powders will result in a compressed powder load, and the compressed powder can reduce/eliminate setback. Check out the data at Nosler's website for powders that will be compressed. Good powders for this are some of Vihtavuori's powders and Accurate #9.

https://load-data.nosler.com/load-data/357-sig/

357 SIG bullets have a short nose compared to other 9mm bullets because they don't protrude very far from the case mouth. It's wise to select bullets with this feature so the bullet ogive does not extend into the case mouth which would reduce the surface contact between the bullet and the case wall, which would in itself reduce neck tension.

I have done the conversion from g27 to 357 sig, but I use a glock 32 barrel (4") instead; I think the 357 sig needs the four inches. The barrel sticks out .6" inches from the g27 slide, but it shoots flawlessly. The 357 sig is freakishly consistent--in 20 rounds of different self-defense loads, I got the same feet per second three times. The average spread across five rounds for each of the four powders is about 7 fps. I have settled on v-crown 125gr and WSF powder, which averages 1375 fps and more than 500 foot pounds of energy.

Check all the discussions about reloading the 357 sig; I first size with a 40 carbide die and then neck size with 357 sig die; I don't flare the case mouth and lightly crimp. Get the right bullets too (long bearing surface).

For me, the 357 sig recoils less than the 40 S&W in the Glock 27 (but I use a polymer80 g27 frame, which fits my hand much better).

I did it with my G23, used a KKM barrel. G23 magazines usually work but I did have a few issues with them so use G2 mags when carrying. Have had good luck with Blue dot powder.

Edited to correct error in saying G19 instead of G23.

tbob38 said:

I did it with my G19, used a KKM barrel.

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Really? I didn't think the breach face on a G19 could accommodate a .40/.357sig case head. Can it?

WrongHanded said:

Really? I didn't think the breach face on a G19 could accommodate a .40/.357sig case head. Can it?

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You are right. It was my Glock 23, that I converted. Sorry!

I've got a G23 with a KKM .357sig conversion barrel and it works like a charm. My understanding is there is no difference in the Glock .40S&W mags and the Glock .357sig mags, so I did not buy the Glock .357sig mags. That said, I also have a KKM 9mm conversion barrel for my G23 and then, yes, absolutely I use Glock 9mm magazines.

I have a Glock 31 which is a 357 SIG .... I got a conversion barrel for 9 mm.... a Glock 22 barrel would make it into a .40 S&W....

I have shot both 9 mm and 357 SIG out the same magazine with out any problems...

Have a LWD 5.3" .357Sig Bbl for my G23.

Shoots HDY Custom 147 gr. XTP at > 1300 fps.

Got a G32 follower, but never had any issues w/ G23 followers and either HDY Custom 147 gr. or S&B 140 gr. TFP.




GR

Give you an idea of factory ammo, these averages are from my pistols:
Glock 33:
Speer Gold Dot 125 gr. @ 1,284 fps / 458# KE
Federal HST 125 gr. @ 1,315 fps / 480# KE
Glock 32:
Speer Gold Dot 125 gr. @ 1,344 fps / 501# KE
Federal HST 125 gr. @ 1,358 fps / 512# KE

l do it all the time,no issues.love it.

Both my 357Sig chambered pistols were originally .40S&W. The conversion, using Storm Lake barrels for both the M&Pc and XDm 4.5 each took less than a minute. Converting them back takes just as long.

I've used the magazines that came with the pistols (I believe both are marked .40S&W/357 Sig IIRC) without a single hiccup. The only difference I can tell while shooting is slightly less recoil and much, much more blast.

I only use Speer Lawman 357Sig for the range and carry Underwood's 125gr Gold Dot. I will likely switch to Underwood's 115gr Extreme Penetrator at some point since both are sometimes used as trail pistols whenever I give the 10mm a break.

I originally intended to reload for the 357Sig but I think I'll stick with reloading straight wall cartridges for now.

bltmonty said:

I have done the conversion from g27 to 357 sig, but I use a glock 32 barrel (4") instead; I think the 357 sig needs the four inches. The barrel sticks out .6" inches from the g27 slide, but it shoots flawlessly. The 357 sig is freakishly consistent--in 20 rounds of different self-defense loads, I got the same feet per second three times. The average spread across five rounds for each of the four powders is about 7 fps. I have settled on v-crown 125gr and WSF powder, which averages 1375 fps and more than 500 foot pounds of energy.

Check all the discussions about reloading the 357 sig; I first size with a 40 carbide die and then neck size with 357 sig die; I don't flare the case mouth and lightly crimp. Get the right bullets too (long bearing surface).

For me, the 357 sig recoils less than the 40 S&W in the Glock 27 (but I use a polymer80 g27 frame, which fits my hand much better).

Click to expand...

I was wondering if the ghost frame poly 80 guns were strong enough for .357 and .40, especially in the short frame 26, 27, and 33.

the poly 80 frames have a larger locking block than Glock oem,and it fits very tightly and well supported. So I tend to think it's stronger. After the first magazine, the sc frame has been flawless in both 40 and 357.