My advice is set aside the steel rod and get the 40cr or 42cr hydraulic tubing listed in the ECM Tutorial document (16mm OD, 8.0 - 8.6mm ID). Then follow the tutorial. Yes, it’s more expensive than stainless steel rod. That’s because it’s actually designed to contain the kind of pressure a 9mm cartridge will produce. The 40cr and 42cr steel is significantly stronger and harder than your stainless steel rod (which is probably 304 or 316 alloy).

I can’t emphasize this enough – taking shortcuts when making a 9mm barrel puts you at high risk of serious injury or even death. If you can’t do it right due to cost or material availability, don’t do it.

You’re going to need a proper lathe and associated tooling, or get into EDM/Electrical Discharge Machining. Either of those processes is going to require a significant time and learning investment to be proficient enough to make a gun barrel.

i have no advice but just wanted to say all you that DIY the whole FGC-9 are on a dif level and i respect tf out of your dedication.