357 Sig Info Needed Reloads and Conversion

[shotslow]

I have bought a Storm Lake 357 Sig barrel for my M&P 40 Pro with a 5 inch barrel. I have the reloading stuff to reload. I purchased a box of Winchester 357 Sig. (price shock) Also I got 200 Starline 357 Sig brass. The barrel drops into my M&P just fine. Now the problems begin.

I made reloads that fit into the barrel using it as a guage and using the factory rounds as a model. I had always thought that the 357 Sig was a 40 S&W necked down to a 9mm. I put the 357 Sig into my S&W 40 guage. They fell through. Not all the way through but past the rim. This is true for both factory and reloads. Will there be extraction problems.

Any other information about what is going on will be appreciated. I can't believe I jumped into this with both eyes closed.

 

[thomasinaz]

I don't think you have a problem yet. I've converted several 40s to 357 sig with only a barrel swap. The guage you're using may index on the lip of the 40 case. The 357 is too small in diameter to stop at the index, and is going in further. The barrel is the best "guage" in my opinion. Shouldn't be a problem. The biggest problem I had was getting the fired cases to full length size, and my reloads wouldn't go completely into the Storm Lake chamber. I had to grind down the top of the RCBS shell holder about .020" and it now sizes perfectly. Also I noticed the 357 cases grow in length after the first firing, so check their length, especially before the first reload. I really enjoy reloading the 357 Sig, it's a very accurate and consistent round.

 

[shotslow]

Excellent. I plan to take it to the range tomorrow and try it out. I will take 10 factory and 50 handloads. I will have the converted 357 sig and the 9mm M&P I use for USPSA. New loads all the way around.

The 357 sig is loaded with a 124 gr Rainier and the lowest recommended grains of Accurate #7. The 9mm is loaded with a 147 gr lead moly bullet and the highest recommended grains of Win231.

I will never shoot 40 S&W and 357 Sig together. I do not want to mix up the brass. I have already ran a 357 sig through my Hornady Progressive while loading 40 S&W. It loads right up. Did lock up in the middle of a USPSA stage.

Thank you for the reply.

 

[GE-Minigun]

.....I will never shoot 40 S&W and 357 Sig together. I do not want to mix up the brass....

Why...the Sig is bottle neck and even Ray Charles could seperate it from the 40. As for firing one in the other...the Sig WILL fire in the 40 but not the other way around...DAMHIK

 

[shotslow]

I picked up a 357 sig brass from a container of 40 S&W and resized it. Felt ok. It then goes into the expander die and is expanded to 40 cal. And loaded. The bottle neck is no longer apparent. It has a 40 caliber bullet in it. However, the ridge of the bottleneck has been pushed out and the cartridge will not lock up in the gun. And would not extract. It was not until I had removed it could I read the head stamp. And see the slight bulge that remained of the bottle neck. You had to look hard and feel. So I will do my best not to have that happen again. I run all the rounds that are used for competition through a gauge now.

BTW just got back from the range. The Storm Lake barrel worked. The factory ammo worked. The sights were on. I wasn't a few times. My handloads worked. Except that some were a millimeter or 2 too long and jammed in the magazine. That's easily fixed. I fired only 22 rounds of 357 sig.

Happy with the barrel and happy with new caliber. Course I really like the M&P 40 Pro plain.

The rest of the range time was spent on the 9mm M&P.

But going to the range tomorrow.

 

[Pardue10]

357 sig

The 357 sig is not necked down from 40. It is different brass. A little longer.

 

[thomasinaz]

Shotslow; I've had very good success with AA#7 in the 357 Sig. I settled on this powder exclusively, for it and the 10MM.

 

[eddie56]

Seems to be thicker as well.Probly to handle the pressure.

 

[shotslow]

Good news Bad news

I went to the indoor range. It's still cold here. Shot the BUG guns I have. Ruger LCR and Glock 36. Fun! Of course, shot the new caliber 357 Sig. It is impressive. Hard to hold on to. Obviously powerful. Grouped well at 15 yards, better than first time. But grouped low. There you have it, good news and bad news.

I will probably end up with adjustable sights. Thats why hitting low is bad news. Dawson Adjustable sight will cost a little over $130. I know this because I put them on my 9mm M&P Pro and am happy with them. Miss the $130 though. I'm going to shoot the 40 a lot before I get the adjustable. I have to get much more besotted by the 357 Sig first. Although it may be too late for me.

I knew the 357 sig brass was not the same as 40 S&W brass. But thanks for mentioning it. That's how I learned about it, along with other info, by reading it in other threads. I was on the internet one day and went and ordered the Storm Lake barrel kinda like being in a candy store and getting candy.

About the Accurate #7: I am very pleased with it. I bought a pound because Accurate is listed in many of the loading manuals for the 357 Sig. I also happen to have a Accurate manual won as a door prize at a Cowboy match. I have used Accurate 5744 in cowboy long range rifle but this is the first pistol powder. (Well, I have Unique but when I bought it, it wasn't called Accurate Powders then. ) The #7 meters great. I will buy more.