Yup nothing over 10" would be factory. Also, just becasue it's a non-factory (custom) job doesn't automatically mean it's worth more. There's a number of companies that have made aftermarket bbls for these guns. Most of the larger or prouder comapanies etched thier name/logo somewhwere on guns they work on.
A few companies now are using sleeved aluminum bbls for these guns.