[jcoaster]

Will a Glock 19 barrel fit a G23, or do you have to get the conversion barrel?

[RottnJP]

It will fit in physically, but should not be used because the breech fit won't be correct, and will give you problems.

Be aware you may have to change the extractor/ejector also if reliability is not adequate with the conversion barrel alone.

If you want 9mm out of your G23, another option is to go to .357 Sig, which uses a 9mm bullet at higher velocity.

The .357 Sig barrel will drop in, and the breech matches the .40 so you won't have any issues with ejector/extractor mismatch.

(The .40 is the parent case for the .357 Sig, so the case head dimensions are identical, which alleviates the potential reliability concerns of going to 9mm in a .40 frame.)

[DannyR]

The G19 barrel is smaller in diameter. It will fit, but using it may damage the slide, the barrel or both. That is why there are aftermarket conversion barrels.

[H3ADHUNT3R]

I personally would just go with the conversion barrel. That way you know its correct and safe.