What is needed for conversion from 9 to .40/.357?

barrel and mag on most guns

Can't scale up, only down. 40 S&W and 357 Sig use same case head. In most cases the extractor will pull the smaller 9mm case head without any problems. However since your gun is set up as 9mm, I do not believe it will work on the larger case head of the 357 Sig and 40 S&W.

For this reason I sold my Glock 26, and then bought a Glock 27 and a conversion barrel.

You might be able to buy a 40 cal upper and keep your lower, not 100% sure.

I went from my M&P 40FS down to 9mm so I'm at the opposite switch.

depends on the design, some extractors can handle the conversion, some guns need the slide changed, and if the slide isn't changed it depends on whether the gun was built on a .40 frame or a 9mm frame, if it's a 9mm, then the barrel maybe be too thin to handle .40, where on a .40 frame the 9mm barrel is heavier than needed, and the same size as a .40 barrel.

I can only speak for myself here. I own the .40 cal FS model M&P and I am purchasing the .357 Sig barrel.
On my gun, the .40 and .357 use the same magazine so I only need to drop in the .357 sig barrel to convert it.
I agree that it's easier to convert down than to convert up.
To go from 9mm to .357 might require a slide, recoil spring, new magazines and barrel for it to work properly.

See #10 below. I duplicated while editing... (Sorry)

Even if a barrel and/or slide change appears to be enough, there are often differences that are not so obvious, like recoil spring strength, feed ramp design, and locking timing that can rise up and create trouble in a conversion that was not intended by the gun's designers.

Jim

It depends ON THE GUN's DESIGN.

You generally can't move up from 9mm (in a gun built for 9mm) to a higher caliber, but you can sometimes move DOWN to 9mm from a larger caliber. It sometimes takes more than a barrel swap when moving down...

The same model gun in a larger caliber will often have a beefier frame, and barrels for the different calibers are sometimes different diameters -- so they won't necessarily fit properly if swapped. To make matters worse, the slides won't always swap, either. (Witness now uses the same frame on all of their guns, so all that's needed to change calibers is a new top end.) As noted above, some other spring changes may be necessary -- but not always.

Companies build "conversion" barrels that allow the larger caliber guns to work with a smaller caliber round. (I have a Glock 23 with the stock .40 barrel, a .357 SIG barrel, and a 9mm conversion barrel. All three can use the same magazine, but that isn't always the case with such conversions.)

Conversion barrels are generally built so that headspace is correct and the extractors work as they should.

Unless you've got one of the guns designed like the Witness line, you're stuck with 9mm, or a .22 kit.

I'll just purchase a new gun and swap the innards I got from APEX into the new one.

Click to expand...

You'll regret that swap... Just buy another set of APEX materials -- as you'll probably end up shooting the 9mm more than the other calibers (and certainly MORE than the .357 SIG).