Can I use a 9 mm conversion barrel in my Pistol in Prod/CO? July 6, 2020 by Jodi Humann D Can I use a 9 mm conversion barrel in my Pistol in Prod/CO? Posted on July 6, 2020 Per the 2020 rules, conversion barrels are now legal in Production and Carry Optics. The restriction that the barrel must be the same caliber as the factory barrel was removed (see App. D4, 21.3 and D7, 21.3). Share this FAQ Back to Top