Ok guys for some reason I seem to really want to try 357 Sig. That said why should I?

By that I mean what are the pros and cons versus 9mm/45?

I know Secret Service uses it, but why only them?

Please enlighten me, as I am genuinely curious about the real world use and applications of this round.

- From the standpoint of terminal ballistics in actual people, it performs the same as 9x19/.40 S&W/.45ACP.
- Being bottlenecked, it has a theoretical advantage in smooth feeding.
- For a given 9x19/.40 S&W based gun, you get the same (reduced) magazine capacity as the .40, without a corresponding gain in terminal ballistic performance. Then again, the same can be said for the .40 S&W versions.
- Having a short neck, bullet setback is a potential problem.
- You get more blast, flash, and recoil (thus, slower followup) than the 9x19, again without a corresponding terminal ballistic gain. I find it similar to shooting .40 S&W. Recoil is obviously less than .45ACP, although blast is significantly greater, which can lead to the perception of increased recoil.  
- Given the higher velocity and smaller diameter bullets, it should be a dandy round for deep penetration, assuming you use bullets designed for deep penetration.

If you like it, by all means go for it. It's fun, but there's nothing remarkable about it: it's basically like having a slightly bigger Tokarev.

9mm ballistics, .40 capacity, 45 cost.

Thank you all for the replies. Kinda what I was figuring. Guess I will stick with 9/45.

In tissue the .357 is indistinguishable. In gel you can sort of see a difference. The only practical advantage to that velocity of penetration of auto bodies. I've seen it used on cars in professionally run ballistics laboratories. It's good at that.

9x23 would be useful.

Windshield glass isn't hard to penetrate but it does cause a lot of deflection. Heavy bullets deflect less. At least that's been my experience. Sheet metal actually causes a lot less deflection which is something LE snipers should know but often don't. The problem with it is there are structural members and supports in car bodies that you can't predict from the outside.

It's got a little more velocity than a standard 9mm since it uses a necked down 40S&W casing. So you have more case capacity for gun powder. You loose some magazine capacity however. The ammo is hard to find and expensive when you do find it. But it's not as rare as some other wildcat calibers. I personally find it to be a very snappy caliber. But it does a better job punching through cars and barriers. If I was in law enforcement I could see using this caliber. But for self defense it's pointless since most self defense situations are so close and they aren't shooting from behind cover. So 9mm makes a much better choice for self defense, less recoil and same projectile and more magazine capacity. For most self defense the 9/40/45 are all good, they are common, easy to shoot, gets the job done. But yeah for barriers .357Sig and 10mm makes more sense, and these are still kind of common, but it's going to be more expensive for sure. All the other wildcat calibers you'll never find in stores and will be expensive. 

It's an angry 9mm.

it cured my nightmares of trying to defend my daughter with a 9mm and the bullet coming slowly out of the barrel and following helplessly on the ground. 
it rocks and rolls

Part of the fun in handguns is choosing your caliber and platform. I own the Glock 31 in .357sig and am happy with it.

The necked cartridge means enhanced feeding reliability... I believe this but I would also point out 9mm is not known to jam in properly maintained and tested guns.

It's bigger than a 9mm, and the goal was to replicate the 125gr .357 magnum load. It sort of replicates a moderate .357 mag load, pushing a 125gr at 1450fps. One difference is the .357 sig hollowpoints cannot have exposelead at the tip like a revolver bullet so the expansion of the bullet is less explosive. To replicate the .357 mag load I've heard it recommended ot use the 115gr Corbon load (or similar), as it will fragment better than a 125gr JHP from a semi-auto.

Some of the factory loads are underloaded, 125gr at 1300-1350fps instead of 1450fps. Do not think they will not perform well though.

The .357 sig is snappy. It has a very fast, sharp recoil. You can control it you just have to be dedicated to practicing. I find 10mm to have easier recoil. The .357 sig is a fast snappy crack, the 10mm is an aggressive thump.

A 10mm can push a 150gr JHP at 1500fps or a 200gr JHP at 1250fps so it wins the 'stopping power' argument in my book. However, you may not be excited about the 10mm or the platforms might not meet your needs.

If you have the money I think it's a nice caliber to support.