There's a .40 to .357sig conversion barrel on ebay, saw one a few weeks ago. Made by Remsport, whoever that is.

I've not done a .40 to .357 conversion on any pistol but shoot it thru a G32 and would love to convert my 9mm shield to .357. But EVERY conversion barrel I've seen is for .40 not 9mm.

I think the barrel forks on the .40 are wider than the 9 so I'd say it won't work. I've searched and found no 9s converted.

You'd need .40 mags as well.

Extractor would probably have to be modified or replaced as well for the larger case size but I'd assume a .40 extractor would drop right in.