I am trying to source a carbine length barrel for conversion of my CMMG Banshee from 8.5" to 16" It's a shame CMMG doesn't offer a carbine length in 9 or .40/10mm. STAG Arms was in the pre-production stage for their new .40/10mm PCC but discontinued it just recently.
Searching high and low to no avail as yet.
Probably gonna be a custom job. There just isn't any meaningful velocity gain to be had after about 10" of barrel length.
Here's the barrel length tests:
http://www.ballisticsbytheinch.com/10mm.html
Now, IF someone was doing handloads and using a slower burning (rifle) powder, he might be able to see more velocity out of it. It's one thing to do that on a single shot or bolt action firearm where you don't have to worry about the round cycling the action, but it's entirely different when you have to tune the round to reliably cycle the action.
Start with one of these and start perfecting your machinist skills:
https://www.gmriflebarrel.com/gp40-40-cal-10mm-23-x-1-raw-barrel-blank-1-16-twist
https://www.gmriflebarrel.com/40-blank-40-cal-10mm-20-x-1-raw-barrel-blank-1-16-twist